Python中的多個內置函數舉例

Python內置函數：

官方幫助文檔：

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

返回數字的絕對值.

def fun(x):

if x < 0:

return -x

return x

print fun(10)
常用函數：

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()

是否是可調用對象

>>> a = 123

>>> callable(a)

False

>>> def a():

...     pass

...

>>> callable(a)

True

>>> class A(object):

...     pass

...

>>> callable(A)

True
type()

判斷類型

>>> type(a)

<type 'function'>
isinstance()

判斷類型,

>>> l =[1,2,3]

>>> isinstance(l,list)

True

>>> isinstance(l,str)

False

>>> isinstance(l,(list,str))

True

判斷是不是一個類

>>> 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，不用時候不在內存中產生值

[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()

轉換成復數

>>> 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()

變為16進制

>>> hex(10)

'0xa'

>>> hex(10L)

'0xaL'

>>> int(0xaL)

10
eval（）

把字符串當成有效表達式求值。

>>> eval('0xaL')

10L

>>> eval("[1,23,'a']")

[1, 23, 'a']
oct()

10進制轉成8進制

>>> oct(10)

'012'

>>> oct(8)

'010'
chr()

查ASSIC碼對應值:

>>> chr(97)

'a'

>>> chr(65)

'A'
ord()

>>> ord('A')

65
字符串處理的函數：

str.capitalize()

首字母變大寫：

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'
序列處理函數：

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).

參數有幾個，函數里的參數也應該對應有幾個

>>> 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
列表表達式：

[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]