python 经典函数

lambda函数和and - or技巧的使用

当collapse为true时，返回" ".join(s.split())，而当collapse为false时，则返回s

processFunc = collapse and (lambda s: " ".join(s.split())) or (lambda s: s)

这个函数主要着重于简单的模糊处理和默认参数处理

def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):
    while True:
        ok = raw_input(prompt)
        if ok in ('y', 'ye', 'yes'):
            return True
        if ok in ('n', 'no', 'nop', 'nope'):
            return False
        retries = retries - 1
        if retries < 0:
            raise IOError('refusenik user')
        print complaint

a,b = b,a+b

>>> def fib(n):    # write Fibonacci series up to n
...     """Print a Fibonacci series up to n."""
...     a, b = 0, 1
...     while a < n:
...         print a,
...         a, b = b, a+b
...
>>> # Now call the function we just defined:
... fib(2000)
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

函数接受和处理无法预计的参数

def cheeseshop(kind, *arguments, **keywords):
    print "-- Do you have any", kind, "?"
    print "-- I'm sorry, we're all out of", kind
    for arg in arguments:
        print arg
    print "-" * 40
    keys = sorted(keywords.keys())
    for kw in keys:
        print kw, ":", keywords[kw]


cheeseshop("Limburger", "It's very runny, sir.",
           "It's really very, VERY runny, sir.",
           shopkeeper='Michael Palin',
           client="John Cleese",
           sketch="Cheese Shop Sketch")


'''
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
client : John Cleese
shopkeeper : Michael Palin
sketch : Cheese Shop Sketch
'''

高级构建列表技巧

>>>alist = [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
>>>alist
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

>>> vec = [[1,2,3], [4,5,6], [7,8,9]]
>>> [num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

矩阵转置

>>> m = [
... [1,2,3],
... [4,5,6],
... [7,8,9]
... ]
>>> n = [[row[i] for row in m] for i in range(3)]
>>> for nn in n:
...     print nn
...
[1, 4, 7]
[2, 5, 8]
[3, 6, 9]
>>>

格式化输出

for x in range(1,10):
    #right
    str1 = '{0:2d} {1:3d} {2:4d}'.format(x, x*x, x*x*x)
    #right
    str2 = str.rjust(repr(x),2)+str.rjust(repr(x*x),3)+str.rjust(repr(x*x*x),4)
    #left
    str3 = str.ljust(repr(x),2)+str.ljust(repr(x*x),3)+str.ljust(repr(x*x*x),4)
    #center
    str4 = str.center(repr(x),2)+str.center(repr(x*x),3)+str.center(repr(x*x*x),5)

    ol = "| %s | %s | %s | %s |" % (str1,str2,str3,str4)
    print ol

运行结果

文件操作应当使用with语句，保证能及时释放文件对象

with open("myfile.txt") as f:
    for line in f:
        print line,