6. Sequence Types — str
, unicode
, list
, tuple
, bytearray
, buffer
, xrange
¶
There are seven sequence types: strings, Unicode strings, lists, tuples, bytearrays, buffers, and xrange objects.
For other containers see the built in dict
and set
classes,
and the collections
module.
String literals are written in single or double quotes: 'xyzzy'
,
"frobozz"
. See strings for more about string literals.
Unicode strings are much like strings, but are specified in the syntax
using a preceding 'u'
character: u'abc'
, u"def"
. In addition
to the functionality described here, there are also string-specific
methods described in the String Methods section. 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,)
.
Bytearray objects are created with the built-in function bytearray()
.
Buffer objects are not directly supported by Python syntax, but can be created
by calling the built-in function buffer()
. They don’t support
concatenation or repetition.
Objects of type xrange are similar to buffers in that there is no specific syntax to
create them, but they are created using the xrange()
function. They don’t
support slicing, concatenation or repetition, and using in
, not in
,
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. In the table, s and t are sequences of the same type; n, i and j 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 |
equivalent to adding s to itself n times | (2) |
s[i] |
ith 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(x) |
index of the first occurrence of x in s | |
s.count(x) |
total number of occurrences of x 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 or Unicode string object the
in
andnot in
operations act like a substring test. In Python versions before 2.3, x had to be a string of length 1. In Python 2.3 and beyond, x may be a string of any length.Values of n less than
0
are treated as0
(which yields an empty sequence of the same type as s). Note that items in the sequence s are not copied; they are referenced multiple times. 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 one-element list containing an empty list, so all three elements of[[]] * 3
are references 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]]
Further explanation is available in the FAQ entry faq-multidimensional-list.
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 that-0
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 < (j-i)/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
.Changed in version 2.4: Formerly, string concatenation never occurred in-place.
6.1. String Methods¶
Below are listed the string methods which both 8-bit strings and
Unicode objects support. Some of them are also available on bytearray
objects.
In addition, Python’s strings support the sequence type methods
described in the Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange section. To output formatted strings
use template strings or the %
operator described in the
String Formatting Operations 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.
For 8-bit strings, this method is locale-dependent.
-
str.
center
(width[, fillchar])¶ Return centered in a string of length width. Padding is done using the specified fillchar (default is a space).
Changed in version 2.4: Support for the fillchar argument.
-
str.
count
(sub[, start[, end]])¶ Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.
-
str.
decode
([encoding[, errors]])¶ Decodes the string using the codec registered for encoding. encoding defaults to the default string encoding. errors may be given to set a different error handling scheme. The default is
'strict'
, meaning that encoding errors raiseUnicodeError
. Other possible values are'ignore'
,'replace'
and any other name registered viacodecs.register_error()
, see section Codec Base Classes.New in version 2.2.
Changed in version 2.3: Support for other error handling schemes added.
Changed in version 2.7: Support for keyword arguments added.
-
str.
encode
([encoding[, errors]])¶ Return an encoded version of the string. Default encoding is the current default string encoding. 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.New in version 2.0.
Changed in version 2.3: Support for
'xmlcharrefreplace'
and'backslashreplace'
and other error handling schemes added.Changed in version 2.7: 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.Changed in version 2.5: Accept tuples as suffix.
-
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. Tab positions occur every tabsize characters (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the string, the current column is set to zero and the string is examined character by character. If the character is a tab (
\t
), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the character is a newline (\n
) or return (\r
), it is copied and the current column is reset to zero. Any other character is copied unchanged and the current column is incremented by one regardless of how the character is represented when printed.>>> '01\t012\t0123\t01234'.expandtabs() '01 012 0123 01234' >>> '01\t012\t0123\t01234'.expandtabs(4) '01 012 0123 01234'
-
str.
find
(sub[, start[, end]])¶ Return the lowest index in the string where substring sub is found within the slice
s[start:end]
. Optional arguments start and end are interpreted as in slice notation. Return-1
if sub is not found.Note
The
find()
method should be used only if you need to know the position of sub. To check if sub is a substring or not, use thein
operator:>>> 'Py' in 'Python' True
-
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.
This method of string formatting is the new standard in Python 3, and should be preferred to the
%
formatting described in String Formatting Operations in new code.New in version 2.6.
-
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.
For 8-bit strings, this method is locale-dependent.
-
str.
isalpha
()¶ Return true if all characters in the string are alphabetic and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
-
str.
isdigit
()¶ Return true if all characters in the string are digits and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
-
str.
islower
()¶ Return true if all cased characters [4]_ in the string are lowercase and there is at least one cased character, false otherwise.
For 8-bit strings, this method is locale-dependent.
-
str.
isspace
()¶ Return true if there are only whitespace characters in the string and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.
-
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.
For 8-bit strings, this method is locale-dependent.
-
str.
isupper
()¶ Return true if all cased characters [4]_ in the string are uppercase and there is at least one cased character, false otherwise.
For 8-bit strings, this method is locale-dependent.
-
str.
join
(iterable)¶ Return a string which is the concatenation of the strings in the iterable iterable. 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 or equal to
len(s)
.Changed in version 2.4: Support for the fillchar argument.
-
str.
lower
()¶ Return a copy of the string with all the cased characters [4]_ converted to lowercase.
For 8-bit strings, this method is locale-dependent.
-
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'
Changed in version 2.2.2: Support for the chars argument.
-
str.
partition
(sep)¶ Split the string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.
New in version 2.5.
-
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. Return-1
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 or equal to
len(s)
.Changed in version 2.4: Support for the fillchar argument.
-
str.
rpartition
(sep)¶ Split the string at the last occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.
New in version 2.5.
-
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.New in version 2.4.
-
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'
Changed in version 2.2.2: Support for the chars argument.
-
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 or-1
, 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. This method uses the universal newlines approach to splitting lines. Line breaks are not included in the resulting list unless keepends is given and true.
Python recognizes
"\r"
,"\n"
, and"\r\n"
as line boundaries for 8-bit strings.For example:
>>> 'ab c\n\nde fg\rkl\r\n'.splitlines() ['ab c', '', 'de fg', 'kl'] >>> 'ab c\n\nde fg\rkl\r\n'.splitlines(True) ['ab c\n', '\n', 'de fg\r', 'kl\r\n']
Unlike
split()
when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:>>> "".splitlines() [] >>> "One line\n".splitlines() ['One line']
For comparison,
split('\n')
gives:>>> ''.split('\n') [''] >>> 'Two lines\n'.split('\n') ['Two lines', '']
-
unicode.
splitlines
([keepends])¶ Return a list of the lines in the string, like
str.splitlines()
. However, the Unicode method splits on the following line boundaries, which are a superset of the universal newlines recognized for 8-bit strings.Representation Description \n
Line Feed \r
Carriage Return \r\n
Carriage Return + Line Feed \v
or\x0b
Line Tabulation \f
or\x0c
Form Feed \x1c
File Separator \x1d
Group Separator \x1e
Record Separator \x85
Next Line (C1 Control Code) \u2028
Line Separator \u2029
Paragraph Separator Changed in version 2.7:
\v
and\f
added to list of line boundaries.
-
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.Changed in version 2.5: Accept tuples as prefix.
-
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'
Changed in version 2.2.2: Support for the chars argument.
-
str.
swapcase
()¶ Return a copy of the string with uppercase characters converted to lowercase and vice versa.
For 8-bit strings, this method is locale-dependent.
-
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 language-independent 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"[A-Za-z]+('[A-Za-z]+)?", ... lambda mo: mo.group(0)[0].upper() + ... mo.group(0)[1:].lower(), ... s) ... >>> titlecase("they're bill's friends.") "They're Bill's Friends."
For 8-bit strings, this method is locale-dependent.
-
str.
translate
(table[, deletechars])¶ Return a copy of the string where all characters occurring in the optional argument deletechars are removed, and the remaining characters have been mapped through the given translation table, which must be a string of length 256.
You can use the
maketrans()
helper function in thestring
module to create a translation table. For string objects, set the table argument toNone
for translations that only delete characters:>>> 'read this short text'.translate(None, 'aeiou') 'rd ths shrt txt'
New in version 2.6: Support for a
None
table argument.For Unicode objects, the
translate()
method does not accept the optional deletechars argument. Instead, it returns a copy of the s where all characters have been mapped through the given translation table which must be a mapping of Unicode ordinals to Unicode ordinals, Unicode strings orNone
. Unmapped characters are left untouched. Characters mapped toNone
are deleted. Note, a more flexible approach is to create a custom character mapping codec using thecodecs
module (seeencodings.cp1251
for an example).
-
str.
upper
()¶ Return a copy of the string with all the cased characters [4]_ converted to uppercase. Note that
str.upper().isupper()
might beFalse
ifs
contains uncased characters or if the Unicode category of the resulting character(s) is not “Lu” (Letter, uppercase), but e.g. “Lt” (Letter, titlecase).For 8-bit strings, this method is locale-dependent.
-
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 or equal to
len(s)
.New in version 2.2.2.
The following methods are present only on unicode objects:
-
unicode.
isnumeric
()¶ Return
True
if there are only numeric characters in S,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.
-
unicode.
isdecimal
()¶ Return
True
if there are only decimal characters in S,False
otherwise. Decimal characters include digit characters, and all characters that can be used to form decimal-radix numbers, e.g. U+0660, ARABIC-INDIC DIGIT ZERO.
6.2. String Formatting Operations¶
String and Unicode objects have one unique built-in operation: the %
operator (modulo). This is also known as the string formatting or
interpolation operator. Given format % values
(where format is a string
or Unicode object), %
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 is a Unicode object, or if any
of the objects being converted using the %s
conversion are Unicode objects,
the result will also be a Unicode object.
If format requires a single argument, values may be a single non-tuple object. [5]_ 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 width 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() ). |
(6) |
'%' |
No argument is converted, results in a '%'
character in the result. |
Notes:
The alternate form causes a leading zero (
'0'
) to be inserted between left-hand 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 left-hand 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.
The
%r
conversion was added in Python 2.0.The precision determines the maximal number of characters used.
If the object or format provided is a
unicode
string, the resulting string will also beunicode
.The precision determines the maximal number of characters used.
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 2.7: %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
.
6.3. XRange Type¶
The xrange
type is an immutable sequence which is commonly used for
looping. The advantage of the xrange
type is that an xrange
object will always take the same amount of memory, no matter the size of the
range it represents. There are no consistent performance advantages.
XRange objects have very little behavior: they only support indexing, iteration,
and the len()
function.
6.4. Mutable Sequence Types¶
List and bytearray
objects support additional operations that allow
in-place modification of the object. Other mutable sequence types (when added
to the language) should also support these operations. Strings and tuples
are immutable sequence types: such objects cannot be modified once created.
The following operations are defined on mutable sequence types (where x is
an arbitrary object):
Operation | Result | Notes |
---|---|---|
s[i] = x |
item i of s is replaced by x | |
s[i:j] = t |
slice of s from i to j is replaced by the contents of the iterable t | |
del s[i:j] |
same as s[i:j] = [] |
|
s[i:j:k] = t |
the elements of s[i:j:k]
are replaced by those of t |
(1) |
del s[i:j:k] |
removes the elements of
s[i:j:k] from the list |
|
s.append(x) |
same as s[len(s):len(s)] =
[x] |
(2) |
s.extend(t) or
s += t |
for the most part the same as
s[len(s):len(s)] = t |
(3) |
s *= n |
updates s with its contents repeated n times | (11) |
s.count(x) |
return number of i‘s for
which s[i] == x |
|
s.index(x[, i[, j]]) |
return smallest k such that
s[k] == x and i <= k <
j |
(4) |
s.insert(i, x) |
same as s[i:i] = [x] |
(5) |
s.pop([i]) |
same as x = s[i]; del s[i];
return x |
(6) |
s.remove(x) |
same as del s[s.index(x)] |
(4) |
s.reverse() |
reverses the items of s in place | (7) |
s.sort([cmp[, key[,
reverse]]]) |
sort the items of s in place | (7)(8)(9)(10) |
Notes:
t must have the same length as the slice it is replacing.
The C implementation of Python has historically accepted multiple parameters and implicitly joined them into a tuple; this no longer works in Python 2.0. Use of this misfeature has been deprecated since Python 1.4.
t can be any iterable object.
Raises
ValueError
when x is not found in s. When a negative index is passed as the second or third parameter to theindex()
method, the list length is added, as for slice indices. If it is still negative, it is truncated to zero, as for slice indices.Changed in version 2.3: Previously,
index()
didn’t have arguments for specifying start and stop positions.When a negative index is passed as the first parameter to the
insert()
method, the list length is added, as for slice indices. If it is still negative, it is truncated to zero, as for slice indices.Changed in version 2.3: Previously, all negative indices were truncated to zero.
The
pop()
method’s optional argument i defaults to-1
, so that by default the last item is removed and returned.The
sort()
andreverse()
methods modify the list in place for economy of space when sorting or reversing a large list. To remind you that they operate by side effect, they don’t return the sorted or reversed list.The
sort()
method takes optional arguments for controlling the comparisons.cmp specifies a custom comparison function of two arguments (list items) which should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument:
cmp=lambda x,y: cmp(x.lower(), y.lower())
. The default value isNone
.key specifies a function of one argument that is used to extract a comparison key from each list element:
key=str.lower
. The default value isNone
.reverse is a boolean value. If set to
True
, then the list elements are sorted as if each comparison were reversed.In general, the key and reverse conversion processes are much faster than specifying an equivalent cmp function. This is because cmp is called multiple times for each list element while key and reverse touch each element only once. Use
functools.cmp_to_key()
to convert an old-style cmp function to a key function.Changed in version 2.3: Support for
None
as an equivalent to omitting cmp was added.Changed in version 2.4: Support for key and reverse was added.
Starting with Python 2.3, the
sort()
method is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).The value n is an integer, or an object implementing
__index__()
. Zero and negative values of n clear the sequence. Items in the sequence are not copied; they are referenced multiple times, as explained fors * n
under Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange.