已知参数数目
#!/usr/bin/python3
import sys
if len(sys.argv) != 3:
sys.exit("Error: Please provide exactly two numbers as arguments")
else:
(num1, num2) = sys.argv[1:]
total = int(num1) + int(num2)
print("{} + {} = {}".format(num1, num2, total))
- 传入Python程序的命令行参数自动保存在
sys.argv列表中 - 让用户知道错误信息是非常好的想法
- 当程序因为错误的使用而终止报错，使用
sys.exit()获取错误信息或者一个自定义状态码 - Python文档 - sys模块
$ ./sum_of_two_numbers.py 2 3
2 + 3 = 5
$ echo $?
0
$ ./sum_of_two_numbers.py 2 3 7
Error: Please provide exactly two numbers as arguments
$ echo $?
1
$ ./sum_of_two_numbers.py 2 'x'
Traceback (most recent call last):
File "./sum_of_two_numbers.py", line 9, in <module>
total = int(num1) + int(num2)
ValueError: invalid literal for int() with base 10: 'x'
$ echo $?
1
变长参数
#!/usr/bin/python3
import sys, pathlib, subprocess
if len(sys.argv) < 2:
sys.exit("Error: Please provide at least one filename as argument")
input_files = sys.argv[1:]
files_not_found = []
for filename in input_files:
if not pathlib.Path(filename).is_file():
files_not_found.append("File '{}' not found".format(filename))
continue
line_count = subprocess.getoutput('wc -l < ' + filename)
print("{0:40}: {1:4} lines".format(filename, line_count))
print("\n".join(files_not_found))
- 当处理的用户输入包含文件名时，最好在处理之前进行检查
- Python文档 - pathlib
$ ./varying_command_line_args.py
Error: Please provide at least one filename as argument
$ echo $?
1
$ #选择性呈现输出
$ ./varying_command_line_args.py *.py
calling_shell_commands.py : 14 lines
for_loop.py : 6 lines
functions_default_arg_value.py : 16 lines
functions.py : 24 lines
hello_world.py : 3 lines
if_elif_else.py : 22 lines
if_else_oneliner.py : 6 lines
shell_command_output_redirections.py : 21 lines
...
$ ./varying_command_line_args.py hello_world.py xyz.py for_loop.py abc.py
hello_world.py : 3 lines
for_loop.py : 6 lines
File 'xyz.py' not found
File 'abc.py' not found
- 如果你的Python版本不是3.4或者更高，使用
os模块而不是pathlib模块进行文件检查
import os
if not os.path.isfile(filename):
sys.exit("File '{}' not found".format(filename))
在代码中使用程序名
#!/usr/bin/python3
import sys, pathlib, subprocess, re
if len(sys.argv) != 2:
sys.exit("Error: Please provide exactly one filename as argument")
program_name = sys.argv[0]
filename = sys.argv[1]
if not pathlib.Path(filename).is_file():
sys.exit("File '{}' not found".format(filename))
if re.search(r'line_count.py', program_name):
lc = subprocess.getoutput('wc -l < ' + filename)
print("No. of lines in '{}' is: {}".format(filename, lc))
elif re.search(r'word_count.py', program_name):
wc = subprocess.getoutput('wc -w < ' + filename)
print("No. of words in '{}' is: {}".format(filename, wc))
else:
sys.exit("Program name '{}' not recognized".format(program_name))
- 基于程序名，同一程序可以用作不同的目的
$ ./line_count.py if_elif_else.py
No. of lines in 'if_elif_else.py' is: 22
$ ln -s line_count.py word_count.py
$ ./word_count.py if_elif_else.py
No. of words in 'if_elif_else.py' is: 73
$ ln -s line_count.py abc.py
$ ./abc.py if_elif_else.py
Program name './abc.py' not recognized
$ wc -lw if_elif_else.py
22 73 if_elif_else.py
命令行开关
#!/usr/bin/python3
import argparse, subprocess
parser = argparse.ArgumentParser()
parser.add_argument('-f', '--file', help="file to be sorted", required=True)
parser.add_argument('-u', help="sort uniquely", action="store_true")
args = parser.parse_args()
if args.u:
subprocess.call(['sort', '-u', args.file, '-o', args.file])
else:
subprocess.call(['sort', args.file, '-o', args.file])
- 使用
argparse模块是一种更简单的方式使得构建的程序像shell命令 - 默认它添加一个help选项
-h（短格式）和--help选项（长格式）处理错误的使用
在这个例子中：
-
-f或--file声明为必需选项，它接受一个参数（文件名） -
-u是一个可选的标记 -
help用于指定展示的文本和选项的帮助信息
$ ./sort_file.py
usage: sort_file.py [-h] -f FILE [-u]
sort_file.py: error: the following arguments are required: -f/--file
$ ./sort_file.py -h
usage: sort_file.py [-h] -f FILE [-u]
optional arguments:
-h, --help show this help message and exit
-f FILE, --file FILE file to be sorted
-u sort uniquely
$ ./sort_file.py -f test_list.txt
$ cat test_list.txt
async_test
basic_test
input_test
input_test
output_test
sync_test
$ ./sort_file.py -f test_list.txt -u
$ cat test_list.txt
async_test
basic_test
input_test
output_test
sync_test
$ ./sort_file.py -f xyz.txt
sort: cannot read: xyz.txt: No such file or directory
- 指定位置参数
#!/usr/bin/python3
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('num1', type=int, help="first number")
parser.add_argument('num2', type=int, help="second number")
args = parser.parse_args()
total = args.num1 + args.num2
print("{} + {} = {}".format(args.num1, args.num2, total))
- 比手动解析
sys.argv更可读的方法，同时提供默认帮助和错误处理 - 需要的类型转换可以在构建参数时指定
$ ./sum2nums_argparse.py
usage: sum2nums_argparse.py [-h] num1 num2
sum2nums_argparse.py: error: the following arguments are required: num1, num2
$ ./sum2nums_argparse.py -h
usage: sum2nums_argparse.py [-h] num1 num2
positional arguments:
num1 first number
num2 second number
optional arguments:
-h, --help show this help message and exit
$ ./sum2nums_argparse.py 3 4
3 + 4 = 7
$ ./sum2nums_argparse.py 3 4 7
usage: sum2nums_argparse.py [-h] num1 num2
sum2nums_argparse.py: error: unrecognized arguments: 7
进一步阅读
