1 python which objects to support traversal?
Iterative protocol supported object, such characteristics of an object is () method supports __next __. List, tuple, dictionary, documents support this feature.
2 and read the file traversal, using function readlines () file elements can be read and placed into a list, but this is not the recommended method of accounting for such a large memory processing, using an iterator only take up a small amount of memory.
F 3 is not a determination target using the statement iterator
iter(f) is f
Returns True, it is, or it is not, use the statement to generate an iterator
F1 = travel (F)
At this point f1 it is already an iterator object
Note: that is, raw file iterator, iter is required to generate a list, in a for loop, will be automatically generated iterator iter, usually use can be called iter () manually generated.
4 Derivation
4.1 the return type, external symbols determined by the statement, such as
[x * 2 for x in data]
Return to the list
4.2 filter conditions, the basic format is:
[x * 2 for x in data if x % 2 == 0]
5 Functions
5.1 Definitions:
def function name (parameter 1, parameter 2, ...): function body
5.2 call:
Function name (actual parameter)
5.3 Variable
global、built-in、enclosure、local
5.5 parameter passing
Immutable types: int, float, string, and other tuples, the operation does not affect the original function value
Variable types: lists, dictionaries, tables, etc., within the function affect the operation of the original value, if you do not affect the original value, you need to use a copy