Python Learning (vi)--iterative, file read-write __python

iterations
Iteration through for...in ... Realize
①list

>>> l=[' Ryan ', ' Rick ', ' Morty ']
>>> for key in L:
    print key


Ryan
Rick
Morty

②tuple

>>> t= (' Ryan ', ' Rick ', ' Morty ')
>>> for key in T:
    print key


Ryan
Rick
Morty

③ string

>>> for K in ' abcdefgh ':
    print K


a
b
c
d
e
f
g
h

④ Dictionary
(Dict storage order is not listed in list order)
Iteration Key:

>>> d={' name01 ': ' Ryan ', ' name02 ': ' Rick ', ' name03 ': ' Morty '}
>>> for key in D:
    print key


name03
name02
name01

Iteration Value:

>>> d={' name01 ': ' Ryan ', ' name02 ': ' Rick ', ' name03 ': ' Morty '}
>>> for value in D.iteritems ():
    Print Value


(' name03 ', ' Morty ')
(' Name02 ', ' Rick ')
(' name01 ', ' Ryan ')

Iterate key and value at the same time:

>>> for Key,value in D.iteritems ():
    print key,value


name03 Morty name02
Rick
name01 Ryan

⑤ simultaneously iterate over multiple variables:

>>> for X,y,z in [(' A ', 1,4), (' B ', 4,8), (' d ', 7,9), (' s ', 5,89)]:
    print x,y,z


a 1 4
B 4 8
D 7 9
s 5 89

⑥ uses the enumerate function to turn a list into an index-element pair:

>>> l=[12,56,789,15,5,89,45,34]
>>> for i,v in Enumerate (L):
    print i,v


0
1 56< C13/>2 789
3
4 5 5 [6] 7
34

⑦ determines whether an object can be iterated:

>>> from collections import iterable
>>> isinstance (' Ryan ', iterable)
True
>> > isinstance (12345,iterable)
False

file read and write

1 open () function
flie_obj = open (filename, mode= ' r ', buffering =-1)

FileName is the incoming filename
Mode is an optional parameter, the default value is R, (' R ' Read, ' W ' Write, ' RB ' read binary file < image, video, etc., ' WB ' writes binary file)
Buffering the default value is-1 (for system default caching), optional parameters (0 means no cache, 1 or greater than 1 for caching a row or a specified buffer size)

>>> f1=open (' F:/data.txt ', ' R ')
>>> print f1.read ()
hello,world!
>>> F1.close ()

>>> f2=open (' F:/data.txt ', ' W ')
>>> f2.write (' ABCDEFG ')
>>> f2.close ()

When reading a non-ASCII text file, you must open it in binary mode and then decode it. such as GBK encoded files:

F=open (' F:/data.txt ', ' R ')
U=f.read (). Decode (' GBK ')
print U
f.close ()

(The contents of the Data.txt file are Chinese)
Or use the Codecs module:

Import codecs
with Codecs.open (' F:/data.txt ', ' r ', ' GBK ') as F:
    print F.read ()

2 ReadLines () function
File_obj.readlines ()
Reads data from a line in a file and returns a list containing line breaks.

3 ReadLine () function
File_obj.readline ()
Reads the first row of data in the file, returning a string;

4 Seek () function
File_obj.seek (Offet, whence=0)
Move the file pointer in the file, from whence (0 for the head of the file, 1 for the current position, and 2 for the tail of the file) to offset bytes;
The whence parameter is optional, and the default value is 0.

5 Split () function
Split (self, sep=none, Maxsplit=none)
Split () function: Specifies the delimiter to split the string, parameter 1 is the specified delimiter, and parameter 2 is the number of separated strings;

s = "40920  8.326976    0.953952    8.326976    0.953952"
print s.split (' \ t ')
print s.split (' t '), 2)

Output:

[' 40920 ', ' 8.326976 ', ' 0.953952 ', ' the ' o ', ' 8.326976 ', ' 0.953952 ']
[' 40920 ', ' 8.326976 ', ' 0.953952\t320\t8.326976\t0.953952 ']

6 strip () function
Intercept all carriage return characters.

file Shutdown

Use try...finally to ensure that files are closed correctly, regardless of error

Try:
    f=open (' F:/data.txt ', ' R ')
    print f.read ()
finally:
    if f:
        F.close ()

Or use the WITH statement:

With open (' F:/data.txt ', ' R ') as F:
    print F.read ()