# Python Learning Summary 18: function Parameter Chapter

Source: Internet
Author: User

1. Determine if a function can be called

`Import math>>> x = 1>>> y = math.sqrt>>> callable (x) False>>> callable (y) True`

Note that the function callable is no longer available in Python 3.0 and needs to be replaced with an expression hasattr (func, __call).

2. function (or Class) interpretation

1) function comment, beginning with "#" comment

2) The document string, which is stored as part of the function if the string is written at the beginning of the function, which is called the document string.

`def Square (x):     ' calculates the square of the number X '    return x*x>>> square.__ doc__'calculates the square of the numberX  '>>> in module main:square (x)    calculates the square of the Number x.`

3. Method of transfer of function parameters

1) passed by function parameter order

`def Hello (greeting, name):     return " %s,%s "% (greeting, name)`
`>>> Hello ('hello'' World') Hello, world `

2) Use keywords and default values

` def  hello_1 (greeting =  " hello  , name = "  world    ):  print   %s,%s   ' %`
`def '  World ' ):     print'%s,%s'%(greeting, name)>>>  Hello_2 ('hi') Hi, World`

3) variable number of parameters

`def print_params (*params):    print  params>>>print_ params ('  testing') ('testing',)>>> Print_params (1, 2, 3) (1, 2, 3)`

As can be seen from the above example, a tuple is printed. If used in conjunction with common parameters

`def Print_ params_2 (title, *params):    print  title    Print  params >>> print_params_2 (' params: ' 1, 2, 3) params: (1, 2, 3)>>> Print_ Params_2 (' Nothing: ') Nothing: ()`

But you can't handle keywords.

`>>>print_params_ 2 ('Hmm ... ', something=42)Traceback (most recent call last):   "<pyshell#60>"in?     2 ('Hmm ... ', something=42)'something'`

4) variable number of parameters, and can handle the keyword

`def print_ Params_3 (* *params)    :print  params>>> print_params_ 3 (x=1 , y=2, z=3) {'z'x'y ': 2}`

A dictionary is returned.

The method of all parameter passing, put together to use

`def Print_ params_4 (x, Y, z=3, *pospar, * *keypar)    :print  x, y,    zprint< /c6> pospar    print  keypar>>> print_params Less (1, 2, 3,  5, 6, 7, foo=l, bar=2 )1 2 3(5, 6, 7) {foo:'bar': 2}>> > Print_params_4 (1, 2)1 2 3() {}`

Python Learning Summary 18: function Parameter Chapter

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