python - 如果没有提供命令行参数，则检测并打印

Question

这是我的程序：

from sys import argv

script, arg1 = argv

def program(usr_input, arg1):
    if(usr_input == arg1):
        print "CLI argument and user input are identical"

    else:
        print "CLI argument and user input aren't identical"

if arg1 != "":
    usr_input = raw_input("enter something: ")
    program(usr_input, arg1)

else:
    print "You have not entered a CLI argument at all."

我得到：

Traceback (most recent call last):
  File "filename.py", line 3, in <module>
    script, arg1 = argv
ValueError: need more than 1 value to unpack

如何检测缺少命令行参数并抛出错误/异常而不是接收此错误？

Answer 1

我建议只检查__main__脚本位置中的程序参数，作为整个应用程序的入口点。

import sys
import os

def program(*args):
    # do whatever
    pass

if __name__ == "__main__":
    try:
        arg1 = sys.argv[1]
    except IndexError:
        print "Usage: " + os.path.basename(__file__) + " <arg1>"
        sys.exit(1)

    # start the program
    program(arg1)

Answer 2

您可以处理异常：

In [6]: def program(argv):
    try:
        script, argv1 = argv
    except ValueError:
        print("value error handled")
   ...:         

In [7]: program(argv)
value error handled

Answer 3

试试这个：

script = argv[0]
try:
    arg1 = argv[1]
except:
    arg1 = ''

Answer 4

你可以在try那里使用一个语句：

#!/usr/bin/env python
#-*- coding:utf-8 -*-

import sys

class MyError(Exception):
    def __init__(self, value):
        self.error_string = value

    def __str__(self):
        return eval(repr(self.error_string))

try:
    script, arg1 = sys.argv

except ValueError:     
    raise MyError, "Not enough arguments"

Answer 5

看到这sys.argv是一个列表，您应该检查列表的长度以确保它是您希望的。您的脚本稍作更改以检查长度：

from sys import argv

def program(usr_input, arg1):
    if(usr_input == arg1):
        print "CLI argument and user input are identical"
    else:
        print "CLI argument and user input aren't identical"

if len(argv)== 2:
    arg1 = argv[1]
    usr_input = raw_input("enter something: ")
    program(usr_input, arg1)
else:
    print "You have not entered a CLI argument at all."