[The Python] file read and write

python file object provides three "read" approach: the Read (), readline () and readlines () . Each method can accept a variable to limit the amount of data read each time.

• read () each read the entire file , the file is typically used content into a string variable. If the file is larger than available memory, to be safe, you can repeatedly call read(size)the method, each read up to size bytes of content.
• readlines () once read the entire file , like .read () the same. .readlines () automatically analyzes the contents of the file into a list of lines , this list can be processed by the structure in ... Python's for ....
• readline () a time to read one line , usually much slower than readlines (). Only when there is not enough memory to read the entire file once, you should use the readline ().

Note : These three methods is the end of each line '\ n' read came in, it does not default to '\ n' removed, we need to manually removed.

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python file object provides two "write" method: the Write ()  and writelines () .

• write () method and a read (), readline () method corresponds to the string is written to the file.
• the writelines () method and the readlines () method corresponding to, but also for the list of operations. It receives a list of strings as arguments, to write them to a file, the newline is not automatically added, therefore, requires an explicit join line breaks .

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About open () mode parameter :

'R': Read

'W': write

'A': Append

'R +' == r + w (readable and writable, if the file exists on the error (IOError))

'W +' == w + r (read and write, the file is created if present)

'A +' == a + r (writable can be added, if there is a file created)

Correspondence, if it is a binary file, you can add a thousand million b:

'RB' 'we' 'baby' 'RB +' 'I +' bitter '+'

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example：

    There are two files, each with many rows ip address, find the same ip address two files:

# coding:utf-8
import bisect

with open('test1.txt', 'r') as f1:# 'with'can close file automaticlly
    list1 = f1.readlines()
for i in range(0, len(list1)):
    list1[i] = list1[i].strip('\n')
with open('test2.txt', 'r') as f2:
    list2 = f2.readlines()
for i in range(0, len(list2)):
    list2[i] = list2[i].strip('\n')

list2.sort()
length_2 = len(list2)
same_data = []
for i in list1:
    pos = bisect.bisect_left(list2, i) #二分法
    if pos < len(list2) and list2[pos] == i:
        same_data.append(i)
same_data = list(set(same_data))#利用set的唯一性去除重复项
print(same_data)

bisect  for ordering  a sorted array module and insertion operations.

A method comprising:

     bisect    bisect_left     bisect_right     insort    insort_left     insort_right

     Which bisect is called bisect_right, insort is called insort_right

 

bisect_left(a, x, lo=0, hi=None)

- an object thereof is to find the value will be inserted position and back, without insertion. If x  is present in a position x in the left return

import bisect

li = [1, 23, 45, 12, 23, 42, 54, 123, 14, 52, 3]
li.sort()
print(li)
print(bisect.bisect_left(li, 3))


result:
[1, 3, 12, 14, 23, 23, 42, 45, 52, 54, 123]
1

insort_left(a, x, lo=0, hi=None)

- inserting the element x in a list, the sort sorted and held. If x is already in a, insert it into the left and right of x.

import bisect

li = [1, 23, 45, 12, 23, 42, 54, 123, 14, 52, 3]
li.sort()
print(li)
bisect.insort_left(li, 3.0)
print(li)

result:

[1, 3, 12, 14, 23, 23, 42, 45, 52, 54, 123]
[1, 3.0, 3, 12, 14, 23, 23, 42, 45, 52, 54, 123]