4. Builtin Types¶
The following sections describe the standard types that are built into the interpreter.
The principal builtin types are numerics, sequences, mappings, classes, instances and exceptions.
Some operations are supported by several object types; in particular,
practically all objects can be compared, tested for truth value, and converted
to a string (with the repr()
function or the slightly different
str()
function). The latter function is implicitly used when an object is
written by the print()
function.
4.1. Truth Value Testing¶
Any object can be tested for truth value, for use in an if
or
while
condition or as operand of the Boolean operations below. The
following values are considered false:
None
False
zero of any numeric type, for example,
0
,0.0
,0j
.any empty sequence, for example,
''
,()
,[]
.any empty mapping, for example,
{}
.instances of userdefined classes, if the class defines a
__bool__()
or__len__()
method, when that method returns the integer zero orbool
valueFalse
. [1]
All other values are considered true — so objects of many types are always true.
Operations and builtin functions that have a Boolean result always return 0
or False
for false and 1
or True
for true, unless otherwise stated.
(Important exception: the Boolean operations or
and and
always return
one of their operands.)
4.2. Boolean Operations — and
, or
, not
¶
These are the Boolean operations, ordered by ascending priority:
Operation  Result  Notes 

x or y 
if x is false, then y, else x  (1) 
x and y 
if x is false, then x, else y  (2) 
not x 
if x is false, then True ,
else False 
(3) 
Notes:
 This is a shortcircuit operator, so it only evaluates the second
argument if the first one is
False
.  This is a shortcircuit operator, so it only evaluates the second
argument if the first one is
True
. not
has a lower priority than nonBoolean operators, sonot a == b
is interpreted asnot (a == b)
, anda == not b
is a syntax error.
4.3. Comparisons¶
There are eight comparison operations in Python. They all have the same
priority (which is higher than that of the Boolean operations). Comparisons can
be chained arbitrarily; for example, x < y <= z
is equivalent to x < y and
y <= z
, except that y is evaluated only once (but in both cases z is not
evaluated at all when x < y
is found to be false).
This table summarizes the comparison operations:
Operation  Meaning 

< 
strictly less than 
<= 
less than or equal 
> 
strictly greater than 
>= 
greater than or equal 
== 
equal 
!= 
not equal 
is 
object identity 
is not 
negated object identity 
Objects of different types, except different numeric types, never compare equal.
Furthermore, some types (for example, function objects) support only a degenerate
notion of comparison where any two objects of that type are unequal. The <
,
<=
, >
and >=
operators will raise a TypeError
exception when
comparing a complex number with another builtin numeric type, when the objects
are of different types that cannot be compared, or in other cases where there is
no defined ordering.
Nonidentical instances of a class normally compare as nonequal unless the
class defines the __eq__()
method.
Instances of a class cannot be ordered with respect to other instances of the
same class, or other types of object, unless the class defines enough of the
methods __lt__()
, __le__()
, __gt__()
, and __ge__()
(in
general, __lt__()
and __eq__()
are sufficient, if you want the
conventional meanings of the comparison operators).
The behavior of the is
and is not
operators cannot be
customized; also they can be applied to any two objects and never raise an
exception.
Two more operations with the same syntactic priority, in
and
not in
, are supported only by sequence types (below).
4.4. Numeric Types — int
, float
, complex
¶
There are three distinct numeric types: integers, floating
point numbers, and complex numbers. In addition, Booleans are a
subtype of integers. Integers have unlimited precision. Floating point
numbers are usually implemented using double
in C; information
about the precision and internal representation of floating point
numbers for the machine on which your program is running is available
in sys.float_info
. Complex numbers have a real and imaginary
part, which are each a floating point number. To extract these parts
from a complex number z, use z.real
and z.imag
. (The standard
library includes additional numeric types, fractions
that hold
rationals, and decimal
that hold floatingpoint numbers with
userdefinable precision.)
Numbers are created by numeric literals or as the result of builtin functions
and operators. Unadorned integer literals (including hex, octal and binary
numbers) yield integers. Numeric literals containing a decimal point or an
exponent sign yield floating point numbers. Appending 'j'
or 'J'
to a
numeric literal yields an imaginary number (a complex number with a zero real
part) which you can add to an integer or float to get a complex number with real
and imaginary parts.
Python fully supports mixed arithmetic: when a binary arithmetic operator has
operands of different numeric types, the operand with the “narrower” type is
widened to that of the other, where integer is narrower than floating point,
which is narrower than complex. Comparisons between numbers of mixed type use
the same rule. [2] The constructors int()
, float()
, and
complex()
can be used to produce numbers of a specific type.
All numeric types (except complex) support the following operations, sorted by ascending priority (operations in the same box have the same priority; all numeric operations have a higher priority than comparison operations):
Operation  Result  Notes  Full documentation 

x + y 
sum of x and y  
x  y 
difference of x and y  
x * y 
product of x and y  
x / y 
quotient of x and y  
x // y 
floored quotient of x and y  (1)  
x % y 
remainder of x / y 
(2)  
x 
x negated  
+x 
x unchanged  
abs(x) 
absolute value or magnitude of x  abs() 

int(x) 
x converted to integer  (3)(6)  int() 
float(x) 
x converted to floating point  (4)(6)  float() 
complex(re, im) 
a complex number with real part re, imaginary part im. im defaults to zero.  (6)  complex() 
c.conjugate() 
conjugate of the complex number c  
divmod(x, y) 
the pair (x // y, x % y) 
(2)  divmod() 
pow(x, y) 
x to the power y  (5)  pow() 
x ** y 
x to the power y  (5) 
Notes:
Also referred to as integer division. The resultant value is a whole integer, though the result’s type is not necessarily int. The result is always rounded towards minus infinity:
1//2
is0
,(1)//2
is1
,1//(2)
is1
, and(1)//(2)
is0
.Not for complex numbers. Instead convert to floats using
abs()
if appropriate.Conversion from floating point to integer may round or truncate as in C; see functions
floor()
andceil()
in themath
module for welldefined conversions.float also accepts the strings “nan” and “inf” with an optional prefix “+” or “” for Not a Number (NaN) and positive or negative infinity.
Python defines
pow(0, 0)
and0 ** 0
to be1
, as is common for programming languages.The numeric literals accepted include the digits
0
to9
or any Unicode equivalent (code points with theNd
property).See http://www.unicode.org/Public/6.0.0/ucd/extracted/DerivedNumericType.txt for a complete list of code points with the
Nd
property.
All numbers.Real
types (int
and float
) also include
the following operations:
Operation  Result  Notes 

math.trunc(x) 
x truncated to Integral  
round(x[, n]) 
x rounded to n digits, rounding half to even. If n is omitted, it defaults to 0.  
math.floor(x) 
the greatest integral float <= x  
math.ceil(x) 
the least integral float >= x 
For additional numeric operations see the math
and cmath
modules.
4.4.1. Bitstring Operations on Integer Types¶
Integers support additional operations that make sense only for bitstrings. Negative numbers are treated as their 2’s complement value (this assumes a sufficiently large number of bits that no overflow occurs during the operation).
The priorities of the binary bitwise operations are all lower than the numeric
operations and higher than the comparisons; the unary operation ~
has the
same priority as the other unary numeric operations (+
and 
).
This table lists the bitstring operations sorted in ascending priority (operations in the same box have the same priority):
Operation  Result  Notes 

x  y 
bitwise or of x and y  
x ^ y 
bitwise exclusive or of x and y  
x & y 
bitwise and of x and y  
x << n 
x shifted left by n bits  (1)(2) 
x >> n 
x shifted right by n bits  (1)(3) 
~x 
the bits of x inverted 
Notes:
 Negative shift counts are illegal and cause a
ValueError
to be raised.  A left shift by n bits is equivalent to multiplication by
pow(2, n)
without overflow check.  A right shift by n bits is equivalent to division by
pow(2, n)
without overflow check.
4.4.2. Additional Methods on Integer Types¶
The int type implements the numbers.Integral
abstract base
class. In addition, it provides one more method:

int.
bit_length
()¶ Return the number of bits necessary to represent an integer in binary, excluding the sign and leading zeros:
>>> n = 37 >>> bin(n) '0b100101' >>> n.bit_length() 6
More precisely, if
x
is nonzero, thenx.bit_length()
is the unique positive integerk
such that2**(k1) <= abs(x) < 2**k
. Equivalently, whenabs(x)
is small enough to have a correctly rounded logarithm, thenk = 1 + int(log(abs(x), 2))
. Ifx
is zero, thenx.bit_length()
returns0
.Equivalent to:
def bit_length(self): s = bin(self) # binary representation: bin(37) > '0b100101' s = s.lstrip('0b') # remove leading zeros and minus sign return len(s) # len('100101') > 6
New in version 3.1:
New in version 3.1.

int.
to_bytes
(length, byteorder, *, signed=False)¶ Return an array of bytes representing an integer.
>>> (1024).to_bytes(2, byteorder='big') b'\x04\x00' >>> (1024).to_bytes(10, byteorder='big') b'\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00' >>> (1024).to_bytes(10, byteorder='big', signed=True) b'\xff\xff\xff\xff\xff\xff\xff\xff\xfc\x00' >>> x = 1000 >>> x.to_bytes((x.bit_length() // 8) + 1, byteorder='little') b'\xe8\x03'
The integer is represented using length bytes. An
OverflowError
is raised if the integer is not representable with the given number of bytes.The byteorder argument determines the byte order used to represent the integer. If byteorder is
"big"
, the most significant byte is at the beginning of the byte array. If byteorder is"little"
, the most significant byte is at the end of the byte array. To request the native byte order of the host system, usesys.byteorder
as the byte order value.The signed argument determines whether two’s complement is used to represent the integer. If signed is
False
and a negative integer is given, anOverflowError
is raised. The default value for signed isFalse
.New in version 3.2:
New in version 3.2.

classmethod
int.
from_bytes
(bytes, byteorder, *, signed=False)¶ Return the integer represented by the given array of bytes.
>>> int.from_bytes(b'\x00\x10', byteorder='big') 16 >>> int.from_bytes(b'\x00\x10', byteorder='little') 4096 >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=True) 1024 >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=False) 64512 >>> int.from_bytes([255, 0, 0], byteorder='big') 16711680
The argument bytes must either support the buffer protocol or be an iterable producing bytes.
bytes
andbytearray
are examples of builtin objects that support the buffer protocol.The byteorder argument determines the byte order used to represent the integer. If byteorder is
"big"
, the most significant byte is at the beginning of the byte array. If byteorder is"little"
, the most significant byte is at the end of the byte array. To request the native byte order of the host system, usesys.byteorder
as the byte order value.The signed argument indicates whether two’s complement is used to represent the integer.
New in version 3.2:
New in version 3.2.
4.4.3. Additional Methods on Float¶
The float type implements the numbers.Real
abstract base
class. float also has the following additional methods.

float.
as_integer_ratio
()¶ Return a pair of integers whose ratio is exactly equal to the original float and with a positive denominator. Raises
OverflowError
on infinities and aValueError
on NaNs.

float.
is_integer
()¶ Return
True
if the float instance is finite with integral value, andFalse
otherwise:>>> (2.0).is_integer() True >>> (3.2).is_integer() False
Two methods support conversion to and from hexadecimal strings. Since Python’s floats are stored internally as binary numbers, converting a float to or from a decimal string usually involves a small rounding error. In contrast, hexadecimal strings allow exact representation and specification of floatingpoint numbers. This can be useful when debugging, and in numerical work.

float.
hex
()¶ Return a representation of a floatingpoint number as a hexadecimal string. For finite floatingpoint numbers, this representation will always include a leading
0x
and a trailingp
and exponent.

classmethod
float.
fromhex
(s)¶ Class method to return the float represented by a hexadecimal string s. The string s may have leading and trailing whitespace.
Note that float.hex()
is an instance method, while
float.fromhex()
is a class method.
A hexadecimal string takes the form:
[sign] ['0x'] integer ['.' fraction] ['p' exponent]
where the optional sign
may by either +
or 
, integer
and fraction
are strings of hexadecimal digits, and exponent
is a decimal integer with an optional leading sign. Case is not
significant, and there must be at least one hexadecimal digit in
either the integer or the fraction. This syntax is similar to the
syntax specified in section 6.4.4.2 of the C99 standard, and also to
the syntax used in Java 1.5 onwards. In particular, the output of
float.hex()
is usable as a hexadecimal floatingpoint literal in
C or Java code, and hexadecimal strings produced by C’s %a
format
character or Java’s Double.toHexString
are accepted by
float.fromhex()
.
Note that the exponent is written in decimal rather than hexadecimal,
and that it gives the power of 2 by which to multiply the coefficient.
For example, the hexadecimal string 0x3.a7p10
represents the
floatingpoint number (3 + 10./16 + 7./16**2) * 2.0**10
, or
3740.0
:
>>> float.fromhex('0x3.a7p10')
3740.0
Applying the reverse conversion to 3740.0
gives a different
hexadecimal string representing the same number:
>>> float.hex(3740.0)
'0x1.d380000000000p+11'
4.4.4. Hashing of numeric types¶
For numbers x
and y
, possibly of different types, it’s a requirement
that hash(x) == hash(y)
whenever x == y
(see the __hash__()
method documentation for more details). For ease of implementation and
efficiency across a variety of numeric types (including int
,
float
, decimal.Decimal
and fractions.Fraction
)
Python’s hash for numeric types is based on a single mathematical function
that’s defined for any rational number, and hence applies to all instances of
int
and fraction.Fraction
, and all finite instances of
float
and decimal.Decimal
. Essentially, this function is
given by reduction modulo P
for a fixed prime P
. The value of P
is
made available to Python as the modulus
attribute of
sys.hash_info
.
CPython implementation detail: Currently, the prime used is P = 2**31  1
on machines with 32bit C
longs and P = 2**61  1
on machines with 64bit C longs.
Here are the rules in detail:
 If
x = m / n
is a nonnegative rational number andn
is not divisible byP
, definehash(x)
asm * invmod(n, P) % P
, whereinvmod(n, P)
gives the inverse ofn
moduloP
. If
x = m / n
is a nonnegative rational number andn
is divisible byP
(butm
is not) thenn
has no inverse moduloP
and the rule above doesn’t apply; in this case definehash(x)
to be the constant valuesys.hash_info.inf
. If
x = m / n
is a negative rational number definehash(x)
ashash(x)
. If the resulting hash is1
, replace it with2
. The particular values
sys.hash_info.inf
,sys.hash_info.inf
andsys.hash_info.nan
are used as hash values for positive infinity, negative infinity, or nans (respectively). (All hashable nans have the same hash value.) For a
complex
numberz
, the hash values of the real and imaginary parts are combined by computinghash(z.real) + sys.hash_info.imag * hash(z.imag)
, reduced modulo2**sys.hash_info.width
so that it lies inrange(2**(sys.hash_info.width  1), 2**(sys.hash_info.width  1))
. Again, if the result is1
, it’s replaced with2
.
To clarify the above rules, here’s some example Python code,
equivalent to the builtin hash, for computing the hash of a rational
number, float
, or complex
:
import sys, math
def hash_fraction(m, n):
"""Compute the hash of a rational number m / n.
Assumes m and n are integers, with n positive.
Equivalent to hash(fractions.Fraction(m, n)).
"""
P = sys.hash_info.modulus
# Remove common factors of P. (Unnecessary if m and n already coprime.)
while m % P == n % P == 0:
m, n = m // P, n // P
if n % P == 0:
hash_ = sys.hash_info.inf
else:
# Fermat's Little Theorem: pow(n, P1, P) is 1, so
# pow(n, P2, P) gives the inverse of n modulo P.
hash_ = (abs(m) % P) * pow(n, P  2, P) % P
if m < 0:
hash_ = hash_
if hash_ == 1:
hash_ = 2
return hash_
def hash_float(x):
"""Compute the hash of a float x."""
if math.isnan(x):
return sys.hash_info.nan
elif math.isinf(x):
return sys.hash_info.inf if x > 0 else sys.hash_info.inf
else:
return hash_fraction(*x.as_integer_ratio())
def hash_complex(z):
"""Compute the hash of a complex number z."""
hash_ = hash_float(z.real) + sys.hash_info.imag * hash_float(z.imag)
# do a signed reduction modulo 2**sys.hash_info.width
M = 2**(sys.hash_info.width  1)
hash_ = (hash_ & (M  1))  (hash & M)
if hash_ == 1:
hash_ == 2
return hash_
4.5. Iterator Types¶
Python supports a concept of iteration over containers. This is implemented using two distinct methods; these are used to allow userdefined classes to support iteration. Sequences, described below in more detail, always support the iteration methods.
One method needs to be defined for container objects to provide iteration support:

container.
__iter__
()¶ Return an iterator object. The object is required to support the iterator protocol described below. If a container supports different types of iteration, additional methods can be provided to specifically request iterators for those iteration types. (An example of an object supporting multiple forms of iteration would be a tree structure which supports both breadthfirst and depthfirst traversal.) This method corresponds to the
tp_iter
slot of the type structure for Python objects in the Python/C API.
The iterator objects themselves are required to support the following two methods, which together form the iterator protocol:

iterator.
__iter__
()¶ Return the iterator object itself. This is required to allow both containers and iterators to be used with the
for
andin
statements. This method corresponds to thetp_iter
slot of the type structure for Python objects in the Python/C API.

iterator.
__next__
()¶ Return the next item from the container. If there are no further items, raise the
StopIteration
exception. This method corresponds to thetp_iternext
slot of the type structure for Python objects in the Python/C API.
Python defines several iterator objects to support iteration over general and specific sequence types, dictionaries, and other more specialized forms. The specific types are not important beyond their implementation of the iterator protocol.
Once an iterator’s __next__()
method raises StopIteration
, it must
continue to do so on subsequent calls. Implementations that do not obey this
property are deemed broken.
4.5.1. Generator Types¶
Python’s generators provide a convenient way to implement the iterator
protocol. If a container object’s __iter__()
method is implemented as a
generator, it will automatically return an iterator object (technically, a
generator object) supplying the __iter__()
and __next__()
methods.
More information about generators can be found in the documentation for
the yield expression.
4.6. Sequence Types — str
, bytes
, bytearray
, list
, tuple
, range
¶
There are six sequence types: strings, byte sequences (bytes
objects),
byte arrays (bytearray
objects), lists, tuples, and range objects. For
other containers see the built in dict
and set
classes, and
the collections
module.
Strings contain Unicode characters. Their literals are written in single or
double quotes: 'xyzzy'
, "frobozz"
. See 字符串与字节的字面值 for more about
string literals. In addition to the functionality described here, there are
also stringspecific methods described in the String Methods section.
Bytes and bytearray objects contain single bytes – the former is immutable
while the latter is a mutable sequence. Bytes objects can be constructed the
constructor, bytes()
, and from literals; use a b
prefix with normal
string syntax: b'xyzzy'
. To construct byte arrays, use the
bytearray()
function.
While string objects are sequences of characters (represented by strings of
length 1), bytes and bytearray objects are sequences of integers (between 0
and 255), representing the ASCII value of single bytes. That means that for
a bytes or bytearray object b, b[0]
will be an integer, while
b[0:1]
will be a bytes or bytearray object of length 1. The
representation of bytes objects uses the literal format (b'...'
) since it
is generally more useful than e.g. bytes([50, 19, 100])
. You can always
convert a bytes object into a list of integers using list(b)
.
Also, while in previous Python versions, byte strings and Unicode strings could be exchanged for each other rather freely (barring encoding issues), strings and bytes are now completely separate concepts. There’s no implicit en/decoding if you pass an object of the wrong type. A string always compares unequal to a bytes or bytearray object.
Lists are constructed with square brackets, separating items with commas: [a,
b, c]
. Tuples are constructed by the comma operator (not within square
brackets), with or without enclosing parentheses, but an empty tuple must have
the enclosing parentheses, such as a, b, c
or ()
. A single item tuple
must have a trailing comma, such as (d,)
.
Objects of type range are created using the range()
function. They don’t
support concatenation or repetition, and using min()
or max()
on
them is inefficient.
Most sequence types support the following operations. The in
and not in
operations have the same priorities as the comparison operations. The +
and
*
operations have the same priority as the corresponding numeric operations.
[3] Additional methods are provided for Mutable Sequence Types.
This table lists the sequence operations sorted in ascending priority (operations in the same box have the same priority). In the table, s and t are sequences of the same type; n, i, j and k are integers.
Operation  Result  Notes 

x in s 
True if an item of s is
equal to x, else False 
(1) 
x not in s 
False if an item of s is
equal to x, else True 
(1) 
s + t 
the concatenation of s and t  (6) 
s * n, n * s 
n shallow copies of s concatenated  (2) 
s[i] 
i‘th item of s, origin 0  (3) 
s[i:j] 
slice of s from i to j  (3)(4) 
s[i:j:k] 
slice of s from i to j with step k  (3)(5) 
len(s) 
length of s  
min(s) 
smallest item of s  
max(s) 
largest item of s  
s.index(i) 
index of the first occurence of i in s  
s.count(i) 
total number of occurences of i in s 
Sequence types also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length. (For full details see Comparisons in the language reference.)
Notes:
When s is a string object, the
in
andnot in
operations act like a substring test.Values of n less than
0
are treated as0
(which yields an empty sequence of the same type as s). Note also that the copies are shallow; nested structures are not copied. This often haunts new Python programmers; consider:>>> lists = [[]] * 3 >>> lists [[], [], []] >>> lists[0].append(3) >>> lists [[3], [3], [3]]
What has happened is that
[[]]
is a oneelement list containing an empty list, so all three elements of[[]] * 3
are (pointers to) this single empty list. Modifying any of the elements oflists
modifies this single list. You can create a list of different lists this way:>>> lists = [[] for i in range(3)] >>> lists[0].append(3) >>> lists[1].append(5) >>> lists[2].append(7) >>> lists [[3], [5], [7]]
If i or j is negative, the index is relative to the end of the string:
len(s) + i
orlen(s) + j
is substituted. But note that0
is still0
.The slice of s from i to j is defined as the sequence of items with index k such that
i <= k < j
. If i or j is greater thanlen(s)
, uselen(s)
. If i is omitted orNone
, use0
. If j is omitted orNone
, uselen(s)
. If i is greater than or equal to j, the slice is empty.The slice of s from i to j with step k is defined as the sequence of items with index
x = i + n*k
such that0 <= n < (ji)/k
. In other words, the indices arei
,i+k
,i+2*k
,i+3*k
and so on, stopping when j is reached (but never including j). If i or j is greater thanlen(s)
, uselen(s)
. If i or j are omitted orNone
, they become “end” values (which end depends on the sign of k). Note, k cannot be zero. If k isNone
, it is treated like1
.CPython implementation detail: If s and t are both strings, some Python implementations such as CPython can usually perform an inplace optimization for assignments of the form
s = s + t
ors += t
. When applicable, this optimization makes quadratic runtime much less likely. This optimization is both version and implementation dependent. For performance sensitive code, it is preferable to use thestr.join()
method which assures consistent linear concatenation performance across versions and implementations.
4.6.1. String Methods¶
String objects support the methods listed below.
In addition, Python’s strings support the sequence type methods described in the
Sequence Types — str, bytes, bytearray, list, tuple, range section. To output formatted strings, see the
String Formatting section. Also, see the re
module for string
functions based on regular expressions.

str.
capitalize
()¶ Return a copy of the string with its first character capitalized and the rest lowercased.

str.
center
(width[, fillchar])¶ Return centered in a string of length width. Padding is done using the specified fillchar (default is a space).

str.
count
(sub[, start[, end]])¶ Return the number of nonoverlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

str.
encode
(encoding="utf8", errors="strict")¶ Return an encoded version of the string as a bytes object. Default encoding is
'utf8'
. errors may be given to set a different error handling scheme. The default for errors is'strict'
, meaning that encoding errors raise aUnicodeError
. Other possible values are'ignore'
,'replace'
,'xmlcharrefreplace'
,'backslashreplace'
and any other name registered viacodecs.register_error()
, see section Codec Base Classes. For a list of possible encodings, see section Standard Encodings.Changed in version 3.1:
Changed in version 3.1: Support for keyword arguments added.

str.
endswith
(suffix[, start[, end]])¶ Return
True
if the string ends with the specified suffix, otherwise returnFalse
. suffix can also be a tuple of suffixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.

str.
expandtabs
([tabsize])¶ Return a copy of the string where all tab characters are replaced by one or more spaces, depending on the current column and the given tab size. The column number is reset to zero after each newline occurring in the string. If tabsize is not given, a tab size of
8
characters is assumed. This doesn’t understand other nonprinting characters or escape sequences.

str.
find
(sub[, start[, end]])¶ Return the lowest index in the string where substring sub is found, such that sub is contained in the slice
s[start:end]
. Optional arguments start and end are interpreted as in slice notation. Return1
if sub is not found.

str.
format
(*args, **kwargs)¶ Perform a string formatting operation. The string on which this method is called can contain literal text or replacement fields delimited by braces
{}
. Each replacement field contains either the numeric index of a positional argument, or the name of a keyword argument. Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument.>>> "The sum of 1 + 2 is {0}".format(1+2) 'The sum of 1 + 2 is 3'
See Format String Syntax for a description of the various formatting options that can be specified in format strings.

str.
format_map
(mapping)¶ Similar to
str.format(**mapping)
, except thatmapping
is used directly and not copied to adict
. This is useful if for examplemapping
is a dict subclass:>>> class Default(dict): ... def __missing__(self, key): ... return key ... >>> '{name} was born in {country}'.format_map(Default(name='Guido')) 'Guido was born in country'
New in version 3.2:
New in version 3.2.

str.
index
(sub[, start[, end]])¶ Like
find()
, but raiseValueError
when the substring is not found.

str.
isalnum
()¶ Return true if all characters in the string are alphanumeric and there is at least one character, false otherwise. A character
c
is alphanumeric if one of the following returnsTrue
:c.isalpha()
,c.isdecimal()
,c.isdigit()
, orc.isnumeric()
.

str.
isalpha
()¶ Return true if all characters in the string are alphabetic and there is at least one character, false otherwise. Alphabetic characters are those characters defined in the Unicode character database as “Letter”, i.e., those with general category property being one of “Lm”, “Lt”, “Lu”, “Ll”, or “Lo”. Note that this is different from the “Alphabetic” property defined in the Unicode Standard.

str.
isdecimal
()¶ Return true if all characters in the string are decimal characters and there is at least one character, false otherwise. Decimal characters are those from general category “Nd”. This category includes digit characters, and all characters that that can be used to form decimalradix numbers, e.g. U+0660, ARABICINDIC DIGIT ZERO.

str.
isdigit
()¶ Return true if all characters in the string are digits and there is at least one character, false otherwise. Digits include decimal characters and digits that need special handling, such as the compatibility superscript digits. Formally, a digit is a character that has the property value Numeric_Type=Digit or Numeric_Type=Decimal.

str.
isidentifier
()¶ Return true if the string is a valid identifier according to the language definition, section 标识符和关键字.

str.
islower
()¶ Return true if all cased characters in the string are lowercase and there is at least one cased character, false otherwise. Cased characters are those with general category property being one of “Lu”, “Ll”, or “Lt” and lowercase characters are those with general category property “Ll”.

str.
isnumeric
()¶ Return true if all characters in the string are numeric characters, and there is at least one character, false otherwise. Numeric characters include digit characters, and all characters that have the Unicode numeric value property, e.g. U+2155, VULGAR FRACTION ONE FIFTH. Formally, numeric characters are those with the property value Numeric_Type=Digit, Numeric_Type=Decimal or Numeric_Type=Numeric.

str.
isprintable
()¶ Return true if all characters in the string are printable or the string is empty, false otherwise. Nonprintable characters are those characters defined in the Unicode character database as “Other” or “Separator”, excepting the ASCII space (0x20) which is considered printable. (Note that printable characters in this context are those which should not be escaped when
repr()
is invoked on a string. It has no bearing on the handling of strings written tosys.stdout
orsys.stderr
.)

str.
isspace
()¶ Return true if there are only whitespace characters in the string and there is at least one character, false otherwise. Whitespace characters are those characters defined in the Unicode character database as “Other” or “Separator” and those with bidirectional property being one of “WS”, “B”, or “S”.

str.
istitle
()¶ Return true if the string is a titlecased string and there is at least one character, for example uppercase characters may only follow uncased characters and lowercase characters only cased ones. Return false otherwise.

str.
isupper
()¶ Return true if all cased characters in the string are uppercase and there is at least one cased character, false otherwise. Cased characters are those with general category property being one of “Lu”, “Ll”, or “Lt” and uppercase characters are those with general category property “Lu”.

str.
join
(iterable)¶ Return a string which is the concatenation of the strings in the iterable iterable. A
TypeError
will be raised if there are any nonstring values in seq, includingbytes
objects. The separator between elements is the string providing this method.

str.
ljust
(width[, fillchar])¶ Return the string left justified in a string of length width. Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than
len(s)
.

str.
lower
()¶ Return a copy of the string converted to lowercase.

str.
lstrip
([chars])¶ Return a copy of the string with leading characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or
None
, the chars argument defaults to removing whitespace. The chars argument is not a prefix; rather, all combinations of its values are stripped:>>> ' spacious '.lstrip() 'spacious ' >>> 'www.example.com'.lstrip('cmowz.') 'example.com'

static
str.
maketrans
(x[, y[, z]])¶ This static method returns a translation table usable for
str.translate()
.If there is only one argument, it must be a dictionary mapping Unicode ordinals (integers) or characters (strings of length 1) to Unicode ordinals, strings (of arbitrary lengths) or None. Character keys will then be converted to ordinals.
If there are two arguments, they must be strings of equal length, and in the resulting dictionary, each character in x will be mapped to the character at the same position in y. If there is a third argument, it must be a string, whose characters will be mapped to None in the result.

str.
partition
(sep)¶ Split the string at the first occurrence of sep, and return a 3tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3tuple containing the string itself, followed by two empty strings.

str.
replace
(old, new[, count])¶ Return a copy of the string with all occurrences of substring old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.

str.
rfind
(sub[, start[, end]])¶ Return the highest index in the string where substring sub is found, such that sub is contained within
s[start:end]
. Optional arguments start and end are interpreted as in slice notation. Return1
on failure.

str.
rindex
(sub[, start[, end]])¶ Like
rfind()
but raisesValueError
when the substring sub is not found.

str.
rjust
(width[, fillchar])¶ Return the string right justified in a string of length width. Padding is done using the specified fillchar (default is a space). The original string is returned if width is less than
len(s)
.

str.
rpartition
(sep)¶ Split the string at the last occurrence of sep, and return a 3tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3tuple containing two empty strings, followed by the string itself.

str.
rsplit
([sep[, maxsplit]])¶ Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep is not specified or
None
, any whitespace string is a separator. Except for splitting from the right,rsplit()
behaves likesplit()
which is described in detail below.

str.
rstrip
([chars])¶ Return a copy of the string with trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or
None
, the chars argument defaults to removing whitespace. The chars argument is not a suffix; rather, all combinations of its values are stripped:>>> ' spacious '.rstrip() ' spacious' >>> 'mississippi'.rstrip('ipz') 'mississ'

str.
split
([sep[, maxsplit]])¶ Return a list of the words in the string, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done (thus, the list will have at most
maxsplit+1
elements). If maxsplit is not specified, then there is no limit on the number of splits (all possible splits are made).If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example,
'1,,2'.split(',')
returns['1', '', '2']
). The sep argument may consist of multiple characters (for example,'1<>2<>3'.split('<>')
returns['1', '2', '3']
). Splitting an empty string with a specified separator returns['']
.If sep is not specified or is
None
, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with aNone
separator returns[]
.For example,
' 1 2 3 '.split()
returns['1', '2', '3']
, and' 1 2 3 '.split(None, 1)
returns['1', '2 3 ']
.

str.
splitlines
([keepends])¶ Return a list of the lines in the string, breaking at line boundaries. Line breaks are not included in the resulting list unless keepends is given and true.

str.
startswith
(prefix[, start[, end]])¶ Return
True
if string starts with the prefix, otherwise returnFalse
. prefix can also be a tuple of prefixes to look for. With optional start, test string beginning at that position. With optional end, stop comparing string at that position.

str.
strip
([chars])¶ Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or
None
, the chars argument defaults to removing whitespace. The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped:>>> ' spacious '.strip() 'spacious' >>> 'www.example.com'.strip('cmowz.') 'example'

str.
swapcase
()¶ Return a copy of the string with uppercase characters converted to lowercase and vice versa.

str.
title
()¶ Return a titlecased version of the string where words start with an uppercase character and the remaining characters are lowercase.
The algorithm uses a simple languageindependent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result:
>>> "they're bill's friends from the UK".title() "They'Re Bill'S Friends From The Uk"
A workaround for apostrophes can be constructed using regular expressions:
>>> import re >>> def titlecase(s): return re.sub(r"[AZaz]+('[AZaz]+)?", lambda mo: mo.group(0)[0].upper() + mo.group(0)[1:].lower(), s) >>> titlecase("they're bill's friends.") "They're Bill's Friends."

str.
translate
(map)¶ Return a copy of the s where all characters have been mapped through the map which must be a dictionary of Unicode ordinals (integers) to Unicode ordinals, strings or
None
. Unmapped characters are left untouched. Characters mapped toNone
are deleted.You can use
str.maketrans()
to create a translation map from charactertocharacter mappings in different formats.Note
An even more flexible approach is to create a custom character mapping codec using the
codecs
module (seeencodings.cp1251
for an example).

str.
upper
()¶ Return a copy of the string converted to uppercase.

str.
zfill
(width)¶ Return the numeric string left filled with zeros in a string of length width. A sign prefix is handled correctly. The original string is returned if width is less than
len(s)
.
4.6.2. Old String Formatting Operations¶
Note
The formatting operations described here are obsolete and may go away in future versions of Python. Use the new String Formatting in new code.
String objects have one unique builtin operation: the %
operator (modulo).
This is also known as the string formatting or interpolation operator.
Given format % values
(where format is a string), %
conversion
specifications in format are replaced with zero or more elements of values.
The effect is similar to the using sprintf()
in the C language.
If format requires a single argument, values may be a single nontuple object. [4] Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).
A conversion specifier contains two or more characters and has the following components, which must occur in this order:
 The
'%'
character, which marks the start of the specifier.  Mapping key (optional), consisting of a parenthesised sequence of characters
(for example,
(somename)
).  Conversion flags (optional), which affect the result of some conversion types.
 Minimum field width (optional). If specified as an
'*'
(asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.  Precision (optional), given as a
'.'
(dot) followed by the precision. If specified as'*'
(an asterisk), the actual precision is read from the next element of the tuple in values, and the value to convert comes after the precision.  Length modifier (optional).
 Conversion type.
When the right argument is a dictionary (or other mapping type), then the
formats in the string must include a parenthesised mapping key into that
dictionary inserted immediately after the '%'
character. The mapping key
selects the value to be formatted from the mapping. For example:
>>> print('%(language)s has %(number)03d quote types.' %
... {'language': "Python", "number": 2})
Python has 002 quote types.
In this case no *
specifiers may occur in a format (since they require a
sequential parameter list).
The conversion flag characters are:
Flag  Meaning 

'#' 
The value conversion will use the “alternate form” (where defined below). 
'0' 
The conversion will be zero padded for numeric values. 
'' 
The converted value is left adjusted (overrides the '0'
conversion if both are given). 
' ' 
(a space) A blank should be left before a positive number (or empty string) produced by a signed conversion. 
'+' 
A sign character ('+' or '' ) will precede the conversion
(overrides a “space” flag). 
A length modifier (h
, l
, or L
) may be present, but is ignored as it
is not necessary for Python – so e.g. %ld
is identical to %d
.
The conversion types are:
Conversion  Meaning  Notes 

'd' 
Signed integer decimal.  
'i' 
Signed integer decimal.  
'o' 
Signed octal value.  (1) 
'u' 
Obsolete type – it is identical to 'd' . 
(7) 
'x' 
Signed hexadecimal (lowercase).  (2) 
'X' 
Signed hexadecimal (uppercase).  (2) 
'e' 
Floating point exponential format (lowercase).  (3) 
'E' 
Floating point exponential format (uppercase).  (3) 
'f' 
Floating point decimal format.  (3) 
'F' 
Floating point decimal format.  (3) 
'g' 
Floating point format. Uses lowercase exponential format if exponent is less than 4 or not less than precision, decimal format otherwise.  (4) 
'G' 
Floating point format. Uses uppercase exponential format if exponent is less than 4 or not less than precision, decimal format otherwise.  (4) 
'c' 
Single character (accepts integer or single character string).  
'r' 
String (converts any Python object using
repr() ). 
(5) 
's' 
String (converts any Python object using
str() ). 
(5) 
'a' 
String (converts any Python object using
ascii() ). 
(5) 
'%' 
No argument is converted, results in a '%'
character in the result. 
Notes:
The alternate form causes a leading zero (
'0'
) to be inserted between lefthand padding and the formatting of the number if the leading character of the result is not already a zero.The alternate form causes a leading
'0x'
or'0X'
(depending on whether the'x'
or'X'
format was used) to be inserted between lefthand padding and the formatting of the number if the leading character of the result is not already a zero.The alternate form causes the result to always contain a decimal point, even if no digits follow it.
The precision determines the number of digits after the decimal point and defaults to 6.
The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.
The precision determines the number of significant digits before and after the decimal point and defaults to 6.
If precision is
N
, the output is truncated toN
characters.
 See PEP 237.
Since Python strings have an explicit length, %s
conversions do not assume
that '\0'
is the end of the string.
Changed in version 3.1:
Changed in version 3.1: %f
conversions for numbers whose absolute value is over 1e50 are no
longer replaced by %g
conversions.
Additional string operations are defined in standard modules string
and
re
.
4.6.3. Range Type¶
The range
type is an immutable sequence which is commonly used for
looping. The advantage of the range
type is that an range
object will always take the same amount of memory, no matter the size of the
range it represents.
Range objects have relatively little behavior: they support indexing, contains,
iteration, the len()
function, and the following methods:

range.
count
(x)¶ Return the number of i‘s for which
s[i] == x
.New in version 3.2:
New in version 3.2.

range.
index
(x)¶ Return the smallest i such that
s[i] == x
. RaisesValueError
when x is not in the range.New in version 3.2:
New in version 3.2.