Python 内建函数

发布时间：2019-06-21 17:36:01编辑：auto阅读（1907）

Python内置函数：

官方帮助文档：

https://docs.python.org/2.7/

    返回数字的绝对值.

    def fun(x):

    if x < 0:

    return -x

    return x

    print fun(10)

常用函数：

abs()

    >>> abs(-100)

    100

取列表最大值和最小值




max()

    >>> max('1235',123)

    '1235'




min()

    >>> min('asdfq3w45')

    '3'




len()

    >>> len('abcdf')

    5

    >>> len([1,3,4,5])

    4

    >>> len((1,3,4,5))

    4

    >>> len({1:3,2:5})

    2




divmod()

    >>> help(divmod)

    Help on built-in function divmod in module __builtin__:

    divmod(...)

    divmod(x, y) -> (quotient, remainder)

    Return the tuple (x//y, x%y).  Invariant: div*y + mod == x.

   

     >>> divmod(5,2)

    (2, 1)




pow()

    pow(...)

    pow(x, y[, z]) -> number

    With two arguments, equivalent to x**y.  With three arguments,

    equivalent to (x**y) % z, but may be more efficient (e.g. for longs).




    >>> pow(2,3)

    8

    >>> pow(2,3,3)

    2




round()

    round(...)

    round(number[, ndigits]) -> floating point number

    Round a number to a given precision in decimal digits (default 0 digits).

    This always returns a floating point number.  Precision may be negative.




    >>> round(12.2)

    12.0

    >>> round(12.23)

    12.0

    >>> round(12.233,2)

    12.23




callable()

是否是可调用对象

    >>> a = 123

    >>> callable(a)

    False

    >>> def a():

    ...     pass

    ...

    >>> callable(a)

    True

    >>> class A(object):

    ...     pass

    ...

    >>> callable(A)

    True




type()

    判断类型

    >>> type(a)

    <type 'function'>




isinstance()

    判断类型,

    >>> l =[1,2,3]

    >>> isinstance(l,list)

    True

    >>> isinstance(l,str)

    False

    >>> isinstance(l,(list,str))

    True

    判断是不是一个类

    >>> A

    <class 'A'>

    >>> a = A()

    >>> a

    <A object at 0x0379BE70>

    >>> isinstance(a,A)

    True




cmp()

    >>> cmp(1,2)

    -1

    >>> cmp(1,0)

    1

    >>> cmp(1,1)

    0

    >>> cmp('a','ab')

    -1

    >>> cmp('a','a')

    0

    >>> cmp('helloa','hello')

    1




range()

    >>> a = range(10)

    >>> a




xrange()

    效率更高，不用时候不在内存中产生值

    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

    >>> b = xrange(10)

    >>> b

    xrange(10)

    >>> for i in b:print i

    ...

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9




int()

    >>> int(123.33)

    123




long()

    >>> long(200)

    200L




float()

    >>> float('123')

    123.0

    >>> float('123.0022')

    123.0022

    >>> float(123.0034)

    123.0034

    >>> float(123)

    123.0




complex()

    转换成复数

    >>> complex(123)

    (123+0j)

    >>> complex(3.1415926)

    (3.1415926+0j)




str()

    >>> str('123')

    '123'




list()

    >>> list('123')

    ['1', '2', '3']




tuple()

    >>> tuple('123')

    ('1', '2', '3')




hex()

    变为16进制

    >>> hex(10)

    '0xa'

    >>> hex(10L)

    '0xaL'

    >>> int(0xaL)

    10




eval（）

    把字符串当成有效表达式求值。

    >>> eval('0xaL')

    10L

    >>> eval("[1,23,'a']")

    [1, 23, 'a']




oct()

    10进制转成8进制

    >>> oct(10)

    '012'

    >>> oct(8)

    '010'




chr()

查ASSIC码对应值:

    >>> chr(97)

    'a'

    >>> chr(65)

    'A'




ord()

    >>> ord('A')

    65




字符串处理的函数：

str.capitalize()

    首字母变大写：

    capitalize(...)

    S.capitalize() -> string

    Return a copy of the string S with only its first character

    capitalized.




    >>> s

    'hello'

    >>> s.capitalize()

    'Hello'

str.replace()

    replace(...)

    S.replace(old, new[, count]) -> string

    Return a copy of string S with all occurrences of substring

    old replaced by new.  If the optional argument count is

    given, only the first count occurrences are replaced.




    >>> s = 'hello,h'

    >>> s.replace('h','H')

    'Hello,H'




split()

    split(...)

    S.split([sep [,maxsplit]]) -> list of strings

    Return a list of the words in the string S, using sep as the

    delimiter string.  If maxsplit is given, at most maxsplit

    splits are done. If sep is not specified or is None, any

    whitespace string is a separator and empty strings are removed

    from the result.




    >>> s = 'hello a\tb\nc'

    >>> s

    'hello a\tb\nc'

    >>> s.split()

    ['hello', 'a', 'b', 'c']

    >> s

    'hello a\tb\nc'

    >>> s.split(' ')

    ['hello', 'a\tb\nc']

    >>> s.split('\t')

    ['hello a', 'b\nc']

    >>> ip = '192.168.1.1'

    >>> ip.split('.')

    ['192', '168', '1', '1']

    >>> ip.split('.',1)

    ['192', '168.1.1']

    >>> ip.split('.',2)

    ['192', '168', '1.1']




join()

    >>> range(10)

    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

    >>> ''.join(str(i) for i in range(10))

    '0123456789'

    >>> int(''.join(str(i) for i in range(10)))

    123456789

string:

    import string

    string.lower

    >>> string.lower('Kfdfa')

    'kfdfa'

    string.upper

    >>> string.upper('Kfdfa')

    'KFDFA'

    string.capitalize()

    >>> string.capitalize('adfafgh')

    'Adfafgh' 

    string.replace()

   >>> string.replace('afkgha','a','A')

    'AfkghA'





序列处理函数：

len()

max()

min()




filter()

    filter(...)

    filter(function or None, sequence) -> list, tuple, or string

    Return those items of sequence for which function(item) is true.  If

    function is None, return the items that are true.  If sequence is a tuple

    or string, return the same type, else return a list.




    >>> filter(None,range(10))

    [1, 2, 3, 4, 5, 6, 7, 8, 9]

    >>> def f(x):

    ...     if x % 2 == 0:

    ...         return True

    ...

    >>> filter(f,range(10))

    [0, 2, 4, 6, 8]

    >>> filter(lambda x: x%2==0,range(10))

    [0, 2, 4, 6, 8]




zip()

    zip(...)

    zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

    Return a list of tuples, where each tuple contains the i-th element

    from each of the argument sequences.  The returned list is truncated

    in length to the length of the shortest argument sequence.




    >>> a1 = [1,3,4]

    >>> a2 = ['a','b','c']

    >>> zip(a1,a2)

    [(1, 'a'), (3, 'b'), (4, 'c')]

    >>> dict(zip(a1,a2))

    {1: 'a', 3: 'b', 4: 'c'}

    >>> dict(zip(a2,a1))

    {'a': 1, 'c': 4, 'b': 3}

    >>> a3 = ['x','y','z']

    >>> zip(a1,a2,a3)

    [(1, 'a', 'x'), (3, 'b', 'y'), (4, 'c', 'z')]

    >>> zip(a1,a3)

    [(1, 'x'), (3, 'y'), (4, 'z')]

    >>> a3 = ['x','y']

    >>> zip(a1,a3)

    [(1, 'x'), (3, 'y')]

    >>> zip(a1,a2,a3)

    [(1, 'a', 'x'), (3, 'b', 'y')]




map()

    map(...)

    map(function, sequence[, sequence, ...]) -> list

    Return a list of the results of applying the function to the items of

    the argument sequence(s).  If more than one sequence is given, the

    function is called with an argument list consisting of the corresponding

    item of each sequence, substituting None for missing values when not all

    sequences have the same length.  If the function is None, return a list of

    the items of the sequence (or a list of tuples if more than one sequence).




    参数有几个，函数里的参数也应该对应有几个

    >>> map(None,a1,a2,a3)

    [(1, 'a', 'x'), (3, 'b', 'y'), (4, 'c', None)]

    >>> def f(x):

    ...     return x**2

    ...

    >>> map(f,a1)

    [1, 9, 16]

    >>> a1

    [1, 3, 4]

    >>> a1

    [1, 3, 4]

    >>> a2

    [2, 5, 6]

    >>> def f(x,y):

    ...     return x*y

    ...

    >>> map(f,a1,a2)

    [2, 15, 24]

    >>> map(lambda x,y: x*y ,range(1,10),range(1,10))

    [1, 4, 9, 16, 25, 36, 49, 64, 81]




reduce()

    reduce(...)

    reduce(function, sequence[, initial]) -> value

    Apply a function of two arguments cumulatively to the items of a sequence,

    from left to right, so as to reduce the sequence to a single value.

    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates

    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items

    of the sequence in the calculation, and serves as a default when the

    sequence is empty.




    >>> def f(x,y):

    ...     return x + y

    ...

    >>> reduce(f,range(1,101))

    5050




列表表达式：




[i*2 for i in range(10)]

    >>> [i*2 for i in range(10)]

    [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

    >>> [i*2+10 for i in range(10)]

    [10, 12, 14, 16, 18, 20, 22, 24, 26, 28]




[i*2+10 for i in range(10) if i%3 == 0]

    >>> [i*2+10 for i in range(10) if i%3 == 0]

    [10, 16, 22, 28]

    

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