argument和parameter的区别:
argument和parameter的区别:
其实跟今天的主题没多大关系, 顺便说一下, 因为看一些英文的技术文章, 会经常用这两个概念.
parameter就相当于java里的"形参":
方法/函数定义时在括号里的参数
def explain_param_vs_arg(param1, param2):
print param1, param2
argument就是所谓"实参":
调用方法/函数时括号里的参数
explain_param_vs_arg("arg1", "arg2")
Positional arguments:
例子:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("echo")
args = parser.parse_args()
print args.echo
输出:
$ python prog.py
usage: prog.py [-h] echo
prog.py: error: the following arguments are required: echo
$ python prog.py --help
usage: prog.py [-h] echo
positional arguments:
echo
optional arguments:
-h, --help show this help message and exit
$ python prog.py foo
foo
上面的例子,基本没什么用. 来个有用点的:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("echo", help="echo the string you use here")
args = parser.parse_args()
print args.echo
输出:
$ python prog.py -h
usage: prog.py [-h] echo
positional arguments:
echo echo the string you use here
optional arguments:
-h, --help show this help message and exit
加了help参数之后, -h就加了对echo这个参数的说明.
来个更有用点的:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", help="display a square of a given number")
args = parser.parse_args()
print args.square**2
输出:
$ python prog.py 4
Traceback (most recent call last):
File "prog.py", line 5, in
print args.square**2
TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'
结果不太理想. 是因为argparse把我们给的参数认成了string. 我们得告诉TA把square当成int来处理:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", help="display a square of a given number",
type=int)
args = parser.parse_args()
print args.square**2
运行结果:
$ python prog.py 4
16
$ python prog.py four
usage: prog.py [-h] square
prog.py: error: argument square: invalid int value: 'four'
这把就对了. 如果参数非法了还会报错.
Optional arguments
前面介绍了positional arguments. 接下来我们看看optional arguments:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--verbosity", help="increase output verbosity")
args = parser.parse_args()
if args.verbosity:
print "verbosity turned on"
输出:
$ python prog.py --verbosity 1
verbosity turned on
$ python prog.py
$ python prog.py --help
usage: prog.py [-h] [--verbosity VERBOSITY]
optional arguments:
-h, --help show this help message and exit
--verbosity VERBOSITY
increase output verbosity
$ python prog.py --verbosity
usage: prog.py [-h] [--verbosity VERBOSITY]
prog.py: error: argument --verbosity: expected one argument
看看都发生了什么:
- 这段代码是想在--verbosity被赋值的时候显示点什么, 没被赋值的时候什么都不显示.
- 所谓optional arguments, 取意译就是"选择性参数". 我们可以看到当不使用--verbosity的时候是不会报错的. args.verbosity的值也是None
- help信息也显示有点不一样. 加了[--verbosity VERSOSITY].
- 当我们使用--verbosity的时候, 就要给TA赋个值, 否则会报错.
上面的例子可以接受任意的整数作为--verbosity的值, 但对我们这简单的小程序来说, 只有俩个值是有用的, True或者False. 我们改一下:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("--verbose", help="increase output verbosity",
action="store_true")
args = parser.parse_args()
if args.verbose:
print "verbosity turned on"
输出:
$ python prog.py --verbose
verbosity turned on
$ python prog.py --verbose 1
usage: prog.py [-h] [--verbose]
prog.py: error: unrecognized arguments: 1
$ python prog.py --help
usage: prog.py [-h] [--verbose]
optional arguments:
-h, --help show this help message and exit
--verbose increase output verbosity
说明:
- 这个选项现在不止是一个需要赋值的flag. 我们甚至给TA改了个名字. 我们还新指定了一个关键字,
action. 同时吧TA赋值成"store_true". 这么做的意思是, 如果使用verbose, 就把True赋值给args.verbose. 如果不使用, 就给TA赋False. - 注意help text也发生了变化.
Short options
如果你经常用terminal命令行模式, 你就会发现我还没说short options. 实现起来其实非常简单.
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-v', '--verbose', help='increase output verbosity',
action='store_true')
args = parser.parse_args()
if args.verbose:
print 'verbosity turned on'
输出:
$ python prog.py -v
verbosity turned on
$ python prog.py --help
usage: prog.py [-h] [-v]
optional arguments:
-h, --help show this help message and exit
-v, --verbose increase output verbosity
可以看到在help text里有对应的改变.
混用positional和optional arguments
让代码来的更复杂点吧:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('square', type=int,
help='display a square of a given number')
parser.add_argument('-v', '--verbose', action='store_true',
help='increase output verbosity')
args = parser.parse_args()
answer = args.square ** 2
if args.verbose:
print 'the square of {} equals {}'.format(args.square, answer)
else:
print answer
输出:
$ python prog.py
usage: prog.py [-h] [-v] square
prog.py: error: the following arguments are required: square
$ python prog.py 4
16
$ python prog.py 4 --verbose
the square of 4 equals 16
$ python prog.py --verbose 4
the square of 4 equals 16
- 我们又把那个positional argument带回来了
- 注意, 赋值的顺序并没影响
我们再把以前的verbosity也带回来:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int, help="display a square of a given number")
parser.add_argument("-v", "--verbosity", type=int, help="increase output verbosity")
args = parser.parse_args()
answer = args.square ** 2
if args.verbosity == 2:
print "the square of {} equals {}".format(args.square, answer)
elif args.verbosity == 1:
print "{}^2 == {}".format(args.square, answer)
else:
print answer
输出:
$ python prog.py 4
16
$ python prog.py 4 -v
usage: prog.py [-h] [-v VERBOSITY] square
prog.py: error: argument -v/--verbosity: expected one argument
$ python prog.py 4 -v 1
4^2 == 16
$ python prog.py 4 -v 2
the square of 4 equals 16
$ python prog.py 4 -v 3
16
看起来都工作的挺好, 除了, 最后好像是有点bug. 我们来通过限定--verbosity来fix它:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
help="display a square of a given number")
parser.add_argument("-v", "--verbosity", type=int, choices=[0, 1, 2], help="increase output verbosity")
args = parser.parse_args()
answer = args.square ** 2
if args.verbosity == 2:
print "the square of {} equals {}".format(args.square, answer)
elif args.verbosity == 1:
print "{}^2 == {}".format(args.square, answer)
else:
print answer
输出:
$ python prog.py 4 -v 3
usage: prog.py [-h] [-v {0,1,2}] square
prog.py: error: argument -v/--verbosity: invalid choice: 3 (choose from 0, 1, 2)
$ python prog.py 4 -h
usage: prog.py [-h] [-v {0,1,2}] square
positional arguments:
square display a square of a given number
optional arguments:
-h, --help show this help message and exit
-v {0,1,2}, --verbosity {0,1,2}
increase output verbosity
可以看到在error message里也反应出我们的改变.
接下来, 我们来看下verbosity的另一种玩法, 这种玩法其实更常见, 更符合cpython使用参数的风格(试试python --verison):
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
help="display the square of a given number")
parser.add_argument("-v", "--verbosity", action="count",
help="increase output verbosity")
args = parser.parse_args()
answer = args.square ** 2
if args.verbosity == 2:
print "the square of {} equals {}".format(args.square, answer)
elif args.verbosity == 1:
print "{}^2 == {}".format(args.square, answer)
else:
print answer
这回我们用了另一个action: "count". 去统计一个optional argument的出现次数.
$ python prog.py 4
16
$ python prog.py 4 -v
4^2 == 16
$ python prog.py 4 -vv
the square of 4 equals 16
$ python prog.py 4 --verbosity --verbosity
the square of 4 equals 16
$ python prog.py 4 -v 1
usage: prog.py [-h] [-v] square
prog.py: error: unrecognized arguments: 1
$ python prog.py 4 -h
usage: prog.py [-h] [-v] square
positional arguments:
square display a square of a given number
optional arguments:
-h, --help show this help message and exit
-v, --verbosity increase output verbosity
$ python prog.py 4 -vvv
16
- 跟前面的
"store_true"一样, 如果不使用, 就会默认赋值为"None". - 这就是
action为"count"的效果. 你们肯定也在其他程序中见过. - 最后的输出还是看起来怪怪的.
我们来fix一下:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
help="display a square of a given number")
parser.add_argument("-v", "--verbosity", action="count",
help="increase output verbosity")
args = parser.parse_args()
answer = args.square ** 2
# bugfix: replace == with >=
if args.verbosity >= 2:
print "the square of {} equals {}".format(args.square, answer)
elif args.verbosity >= 1:
print "{}^2 == {}".format(args.square, answer)
else:
print answer
来看看结果:
$ python prog.py 4 -vvv
the square of 4 equals 16
$ python prog.py 4 -vvvv
the square of 4 equals 16
$ python prog.py 4
Traceback (most recent call last):
File "prog.py", line 11, in
if args.verbosity >= 2:
TypeError: unorderable types: NoneType() >= int()
- 从前两个输出看起来工作的不错, fix了我们的bug.
- 但从最后一个输出看工作的不怎么理想啊...
继续fix:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("square", type=int,
help="display a square of a given number")
parser.add_argument("-v", "--verbosity",
action="count", default=0, help="increase output verbosity")
args = parser.parse_args()
answer = args.square ** 2
if args.verbosity >= 2:
print "the square of {} equals {}".format(args.square, answer)
elif args.verbosity >= 1:
print "{}^2 == {}".format(args.square, answer)
else:
print answer
我们这里介绍了另一个keyword, default. 用了default就会把默认值设置成0. 一定要记住如果不给positional argument赋值, 默认的就会赋值为None. 是不能跟数字做比较的.
$ python prog.py 4
16
目前介绍的功能已经能应付很多情况了. 在结束之前, 我们再来点更猛的吧.
更高级的用法
我们扩展一下这个例子, 来显示更多内容:
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("x", type=int, help="the base")
parser.add_argument("y", type=int, help="the exponent")
parser.add_argument("-v", "--verbosity", action="count", default=0)
args = parser.parse_args()
answer = args.x ** args.y
if args.verbosity >= 2:
print "Running '{}'".format(__file__)
if args.verbosity >= 1:
print "{}^{} == {}".format(args.x, args.y, answer)
print answer
输出:
$ python prog.py
usage: prog.py [-h] [-v] x y
prog.py: error: the following arguments are required: x, y
$ python prog.py -h
usage: prog.py [-h] [-v] x y
positional arguments:
x the base
y the exponent
optional arguments:
-h, --help show this help message and exit
-v, --verbosity
$ python prog.py 4 2 -v
4^2 == 16
$ python prog.py 4 2 -v
4^2 == 16
$ python prog.py 4 2 -vv
Running 'prog.py'
4^2 == 16
处理冲突
我们在例子中加一个argument: --quiet. quiet表示如果不想用verbose的显示方式就用quiet. 它们是互斥的关系. 我们可以这么实现:
import argparse
parser = argparse.ArgumentParser()
group = parser.add_mutually_exclusive_group()
group.add_argument("-v", "--verbose", action="store_true")
group.add_argument("-q", "--quiet", action="store_true")
parser.add_argument("x", type=int, help="the base")
parser.add_argument("y", type=int, help="the exponent")
args = parser.parse_args()
answer = args.x ** args.y
if args.quiet:
print answer
elif args.verbose:
print "{} to the power {} equals {}".format(args.x, args.y, answer)
else:
print "{}^{} == {}".format(args.x, args.y, answer)
输出:
$ python prog.py 4 2
4^2 == 16
$ python prog.py 4 2 -q
16
$ python prog.py 4 2 -v
4 to the power 2 equals 16
$ python prog.py 4 2 -vq
usage: prog.py [-h] [-v | -q] x y
prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose
$ python prog.py 4 2 -v --quiet
usage: prog.py [-h] [-v | -q] x y
prog.py: error: argument -q/--quiet: not allowed with argument -v/--verbose
最后, 如果你想告诉用户程序的主要目的. 可以这么来:
import argparse
parser = argparse.ArgumentParser(description="calculate X to the power of Y")
group = parser.add_mutually_exclusive_group()
group.add_argument("-v", "--verbose", action="store_true")
group.add_argument("-q", "--quiet", action="store_true")
parser.add_argument("x", type=int, help="the base")
parser.add_argument("y", type=int, help="the exponent")
args = parser.parse_args()
answer = args.x ** args.y
if args.quiet:
print answer
elif args.verbose:
print "{} to the power {} equals {}".format(args.x, args.y, answer)
else:
print "{}^{} == {}".format(args.x, args.y, answer)
输出:
$ python prog.py --help
usage: prog.py [-h] [-v | -q] x y
calculate X to the power of Y
positional arguments:
x the base
y the exponent
optional arguments:
-h, --help show this help message and exit
-v, --verbose
-q, --quiet
作者：Edward_f0cus
链接：https://www.jianshu.com/p/a50aead61319
來源：简书
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