Python从另一个文件中删除不匹配的文件行

Question

我有两个文件，第一个包含必要数据：1st file，第二个包含要保留的行列表：2nd file

我尝试通过python代码进行过滤：

import os.path

# loading the input files
output    = open('descmat.txt', 'w+')
input     = open('descmat_all.txt', 'r')
lists      = open('training_lines.txt', 'r')
print "Test1"

# reading the input files
list_lines = lists.readlines()
list_input = input.readlines()

print "Test2"
output.write(list_input[0])

for i  in range(len(list_lines)):
    for ii in range(len(list_input)):
        position = list_input[ii].find(list_lines[i][:-1])
        if position > -1:
            output.write(list_input[ii])
        break 

print "Test3"
output.close()

但此脚本找不到任何匹配项。仅保留第一个文件中与第二个文件匹配的行的最简单解决方案是什么？

Answer 1

替换这部分代码：

for i  in range(len(list_lines)):
    for ii in range(len(list_input)):
        position = list_input[ii].find(list_lines[i][:-1])
        if position > -1:
            output.write(list_input[ii])
        break 

通过这个：

for i  in range(len(list_lines)):
    for ii in range(len(list_input)):
        if list_input[ii][:26] == list_lines[i][:-1]:
            output.write(list_input[ii])

正是我需要的。

Answer 2

如果您将文件都读入一个列表，您可以简单地比较这些列表。看看here 怎么做。 out 应该包含一个可以匹配的字符串列表。

out = [e for e in list_input for i in list_lines if e.startswith(i)]
output.writelines(out)

Answer 3

对于这类问题，Python 有set 数据类型

# prepare a set of normalised training lines
# stripping new lines avoids possible problems with the last line

OK_lines = set(line.rstrip('\n') for line in open('training_lines.txt'))

# when you leave a with block, all the resources are released
# i.e., no need for file.close()

with open('descmat_all.txt') as infile:
    with open('descmat.txt', 'w') as outfile:
        for line in infile:
            # OK_lines have been stripped, input lines must be stripped as well
            if line.rstrip('\n') in OK_lines:
                outfile.write(line)

一个简单的测试

boffi@debian:~/Documents/tmp$ cat check.py 
# prepare a set of normalised training lines
# stripping new lines avoids possible problems with the last line

OK_lines = set(line.rstrip('\n') for line in open('training_lines.txt'))

# when you leave a with block, all the resources are released
# i.e., no need for file.close()

with open('descmat_all.txt') as infile:
    with open('descmat.txt', 'w') as outfile:
        for line in infile:
            # OK_lines have been stripped, input lines must be stripped as well
            if line.rstrip('\n') in OK_lines:
                outfile.write(line)

boffi@debian:~/Documents/tmp$ cat training_lines.txt 
ada
bob
boffi@debian:~/Documents/tmp$ cat descmat_all.txt 
bob
doug
ada
doug
eddy
ada
bob
boffi@debian:~/Documents/tmp$ python check.py
boffi@debian:~/Documents/tmp$ cat descmat.txt 
bob
ada
ada
bob
boffi@debian:~/Documents/tmp$