Python 内建函数
Python内置函数：
官方帮助文档：
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]