Some Python knowledge points

0. New and old

Two kinds of reverse

>>> L = [1,2,3,4]#  New Object>>> r[4, 3, 2, 1]# in place >>> l[4, 3, 2, 1]>>>

Two kinds of sort

# New Object [' Black ', ' blue ', ' green ', ' red ', 'white ' >>> r[' white ', ' black ', ' green ', ' blue ', ' red '] # in-place>>> r[' black ', ' blue ', ' green ', ' red ', ' white '

1. Function parameters

def F (A, B, c=0, *ARGC, **kw):
Print A, B, C, argc, KW

>>> f (1, 2, 3, ' A ', ' B ', ' C ', key= ' value ')
1 2 3 (' A ', ' B ', ' C ') {' key ': ' Value '}

A, B is required parameter, c default parameter, argc variable parameter, kw is the keyword parameter. When the function is passed in, ARGC is a tuple,kw of Dict.

Note The default parameter, be sure to point to the immutable variable. The same parameter of multiple functions may point to the same instance

>>>defFoo (bar=[]): ..... bar.append ("Baz") ...    returnBar>>>foo () ["Baz"]>>>foo () ["Baz","Baz"]>>>foo () ["Baz","Baz","Baz"]>>>defFoo (bar=None): .....ifBar isNone:#or if not bar:... bar =[] ... bar.append ("Baz")...    returnBar ...>>>foo () ["Baz"]>>>foo () ["Baz"]>>>foo () ["Baz"]

2. Iteration

• Determine if you can iterate, use iterable

 from Import iterable>>> isinstance ('string', iterable) True>>> Isinstance ([Isinstance], iterable) True>>> (123, iterable) False

• Introduction of subscript, available enumerate

 for  in Enumerate (['a''b''C' ]):...      Print I, v ... 0 A1 b2 c>>>

• Iterate multiple lists at the same time, using function zip

 for  in Zip ([All-in-a-d], ['a'b''c' ]):...      Print I, J ... 1 a2 b3 C

3. If-else in list comprehension

>>> L = ['We',' is', 42,'ALONE','!']>>> [S.lower ()ifIsinstance (S,STR)ElseS forSinchL] ['We',' is', 42,'alone','!']

4. Class

Http://www.toptal.com/python/python-class-attributes-an-overly-thorough-guide

Qualify members of Class

__slots__

class Student (object): ...      __slots__ = ('name'' age') ...

5. Exception

Check for multiple exceptions and need to be placed within a tuple

Try :...      = ["a""b"] ...     Int (l[2except  (ValueError, Indexerror) as     e: ... Pass ... >>>

Some Python knowledge points