在python中循環瀏覽文本文件行

Question

我有兩個文本文件，我想逐行閱讀並檢查是否發生匹配，如果匹配，則打印或不執行任何操作。 但是在以下代碼中，它僅檢查第一個文件的第一行，並檢查第二個循環文件​​的所有行。 但是我想檢查第一個文件以及第二個文件的所有行。 我不確定自己在犯什么錯誤。

with open("changed_commands_from_default_value", "a") \
            as changed_commands_from_default_value, \
     open(command_file, "r") \
            as command_executed_file, \
     open("default_command_values", "r") \
            as default_command_values:
    for default_command in default_command_values:
       for command_executed in command_executed_file:
           only_command = command_executed.split()[0]
           only_default_command = default_command.split()[0]
           if only_command == only_default_command:
               if command_executed != default_command:
                   print("   > The default value " +
                         default_command.rstrip() + " is changed to " +
                         command_executed.rstrip())
                   changed_commands_from_default_value.write(
                       "The default value " + '"' + default_command + '"' +
                       "is changed to " + '"' + command_executed + '"')

我的數據就像

File 1:

Data1 1
Data2 2
Data3 3
Data4 6
Data5 10

File 2:

Data1 4
Data2 4
Data3 6
....

我想有一個輸出

Data1 is changed from 1 to 4
Data2 is changed from 2 to 4 and so on...

Answer 1

要在兩個迭代器上“並行”循環，請使用內置的zip ，或者在Python 2中使用itertools.izip （當然，后者需要在模塊開始時import itertools ）。

例如，更改：

        for default_command in default_command_values:
            for command_executed in command_executed_file:

變成：

        for default_command, command_executed in zip(
            default_command_values, command_executed_file):

假設這兩個文件確實是“平行的”-即以1-1對應的方式逐行顯示。 如果不是這種情況，那么最簡單的方法（除非文件太大，以至於您的內存無法容納它）是首先將一個讀入dict ，然后遍歷另一個使用dict檢查。 因此，例如：

    cmd2val = {}
    with open("default_command_values", "r") as default_command_values:
        for default_command in default_command_values:
            cmd2val[default_command.split()[0]] = default_command.strip()

然后，分別：

with open(command_file, "r") as command_executed_file:
    for command_executed in command_executed_file:
        only_command = command_executed.split()[0]
        if only_command not in cmd2val: continue   # or whatever
        command_executed = command_executed.strip()
        if command_executed != cmd2val[only_command]:
            # etc, etc, for all output you desire in this case

反之亦然，從預期較小的文件中構建字典，然后使用它逐行檢查預期較大的文件。

Answer 2

只需將讀取置於同一循環中即可。 兩個文件（分別名為t1.in和t2.in）的最小工作示例為：

with open('t1.in', 'r') as f1:
    with open('t2.in', 'r') as f2:
        while True:
        l1, l2 = f1.readline(), f2.readline() # read lines simultaneously

        # handle case where one of the lines is empty 
        # as file line count may differ
        if (not l1) or (not l2): break
        else: 
            # process lines here

本示例同時從兩個文件中讀取行，並且如果其中一個文件的行少於另一個min(lines_of_file_1, lines_of_file_2)讀取min(lines_of_file_1, lines_of_file_2)行。

Answer 3

這是@Alex Martelli的dict建議的實現 ：

#!/usr/bin/env python3
"""Match data in two files. Print the changes in the matched values.

Usage: %(prog)s <old-file> <new-file>
"""
import sys

if len(sys.argv) != 3:
    sys.exit(__doc__ % dict(prog=sys.argv[0]))

old_filename, new_filename = sys.argv[1:]

# read old file
data = {}
with open(old_filename) as file:
    for line in file:
        try:
            key, value = line.split()
            data[key] = int(value)
        except ValueError:
            pass # ignore non-key-value lines

# compare with the new file
with open(new_filename) as file:
    for line in file:
        columns = line.split()
        if len(columns) == 2 and columns[0] in data:
            try:
                new_value = int(columns[1])
            except ValueError:
                continue # ignore invalid lines
            else: # matching line
                value = data[columns[0]]
                if value != new_value: # but values differ
                    print('{key} is changed from {value} to {new_value}'.format(
                        key=columns[0], value=value, new_value=new_value))

輸出（用於問題的輸入）

Data1 is changed from 1 to 4
Data2 is changed from 2 to 4
Data3 is changed from 3 to 6