Question

我创建了一个简单的应用程序，它打印出/etc/passwd输出的可读信息，但在解析文件中的大多数条目后收到错误消息：

Traceback (most recent call last):
  File "unpacking_args5.py", line 19, in <module>
    uname, *fields, homedir, sh = user_info
ValueError: need more than 1 values to unpack

以下是代码：

import subprocess

# the return command output is a string because
# of universal_newlines set to True
output = subprocess.check_output(
            ['cat', '/etc/passwd'],
            universal_newlines = True
        )

# this command converts it into a list of user information on the system
output = output.split('\n')

# --------------------- If this is the value passed there's no error ---- #
# output = [
#     'ianhxc:x:1000:1000:ianHxc,,,:/home/ianhxc:/usr/bin/zsh'
# ]

for line in output:
    user_info = line.strip().split(":")
    uname, *fields, homedir, sh = user_info

    print('Uname: %s' % uname)
    print('Fields: %s' % fields)
    print('homedir: %s' % homedir)
    print('shell: %s' % (sh or 'None'))
    print('')

这是命令的输出：

Uname: root
Fields: ['x', '0', '0', 'root']
homedir: /root
shell: /bin/bash

Uname: daemon
Fields: ['x', '1', '1', 'daemon']
homedir: /usr/sbin
shell: /usr/sbin/nologin

# ... many successful entries omitted ...

Uname: mysql
Fields: ['x', '999', '999', '']
homedir: /home/mysql
shell: None

Traceback (most recent call last):
  File "unpacking_args5.py", line 19, in <module>
    uname, *fields, homedir, sh = user_info
ValueError: need more than 1 values to unpack

我认为这与使用“明星运营商”有关。

Answer 1

你的行中没有:冒号;分割这些时，你只需要一个元素。

这可能是对其进行#评论的行，例如：

>>> line = '#\n'
>>> user_info = line.strip().split(":")
>>> user_info
['#']
>>> uname, *fields, homedir, sh = user_info
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: need more than 1 values to unpack

你可以跳过这些线;测试user_info列表的长度：

for line in output:
    user_info = line.strip().split(":")
    if len(user_info) < 3:
        continue  # not enough fields to be valid
    uname, *fields, homedir, sh = user_info
    # etc.

请注意，在此使用subprocess overkill ;您也可以直接阅读文件：

with open('/etc/passwd') as output:
    for line in output:
        user_info = line.strip().split(":")
        if len(user_info) < 3:
            continue  # not enough fields to be valid
        uname, *fields, homedir, sh = user_info
        # etc.

Answer 2

在出现错误时，user_info未包含足够的元素来分配给uname，fields，homedir和sh。将该赋值语句放入try / except块并让except块打印出user_info，这样您就可以找出使其窒息的输入。

ValueError：在解析/ etc / passwd时需要多个值来解压缩

2 个答案: