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<h1>Argparse 教學<a class="headerlink" href="#argparse-tutorial" title="本標題的永久連結">¶</a></h1>

<tr class="field-odd field"><th class="field-name">author:</th><td class="field-body">Tshepang Lekhonkhobe</td>

</tr>

</tbody>

</table>

這個教學傾向簡介 Python 官方標準含式庫中推薦的命令列解析模組 <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a>。

備註

另外兩個具有同樣功能的模組 <a class="reference internal" href="../library/getopt.html#module-getopt" title="getopt: Portable parser for command line options; support both short and long option names."><code class="xref py py-mod docutils literal notranslate">getopt</code></a> （一個相等於 C 語言中的 <code class="xref c c-func docutils literal notranslate">getopt()</code>）以及被棄用的 <a class="reference internal" href="../library/optparse.html#module-optparse" title="optparse: Command-line option parsing library.(已棄用)"><code class="xref py py-mod docutils literal notranslate">optparse</code></a>。而 <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> 也是根據 <a class="reference internal" href="../library/optparse.html#module-optparse" title="optparse: Command-line option parsing library.(已棄用)"><code class="xref py py-mod docutils literal notranslate">optparse</code></a> 為基礎發展而來，因此有非常近似的使用方式。

</div>

藉由命令 ls 的使用開始這些功能的介紹：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ ls

cpython devguide prog.py pypy rm-unused-function.patch

$ ls pypy

ctypes_configure demo dotviewer include lib_pypy lib-python ...

$ ls -l

total 20

drwxr-xr-x 19 wena wena 4096 Feb 18 18:51 cpython

drwxr-xr-x 4 wena wena 4096 Feb 8 12:04 devguide

-rwxr-xr-x 1 wena wena 535 Feb 19 00:05 prog.py

drwxr-xr-x 14 wena wena 4096 Feb 7 00:59 pypy

-rw-r--r-- 1 wena wena 741 Feb 18 01:01 rm-unused-function.patch

$ ls --help

Usage: ls [OPTION]... [FILE]...

List information about the FILEs (the current directory by default).

Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

...

</pre></div>

</div>

我們可以從四個命令中可以學到的幾個概念：

<li>命令 ls 在執行時不用其他參數就可以顯示出當前目錄底下的內容。</li>

<li>根據這樣的概念延伸後來舉個例子，如果我們想秀出一個不在目錄的資料夾 <code class="docutils literal notranslate">pypy</code> 的內容。我們可以在命令後加上一個位置參數。會用位置參數這樣的名稱是因為程式會知道輸入的參數該做的事情。這樣的概念很像另一個命令 cp，基本的使用方式是 <code class="docutils literal notranslate">cp SRC DEST</code>。第一個位置參數代表的是想要複製的目標，第二個位置的參數代表的則是想要複製到的地方。</li>

<li>現在我們想再增加一些，要顯示除了檔名之外更多的資訊。在這裡就可以選擇加上 <code class="docutils literal notranslate">-l</code> 這個參數。</li>

<li>這是 help 文件的片段。對於以前從未使用過的程序來說非常有用，可以透過這些 help 文件來了解這些該怎麼使用。</li>

</ul>

</div>

我們以一個很簡單的例子開始下面的介紹：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.parse_args()

</pre></div>

</div>

下面是運行這些代碼的結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py

$ python3 prog.py --help

usage: prog.py [-h]

optional arguments:

-h, --help show this help message and exit

$ python3 prog.py --verbose

usage: prog.py [-h]

prog.py: error: unrecognized arguments: --verbose

$ python3 prog.py foo

usage: prog.py [-h]

prog.py: error: unrecognized arguments: foo

</pre></div>

</div>

接者是發生的情況：

<li>運行這個腳本而沒有給與任何參數時就不會顯示任何東西至標準輸出畫面上。這裡並不是這麼的有用。</li>

<li>第二個我們呈現出了 <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> 模組的用處。我們幾乎沒有做什麼事情，但已經得到一個很好的幫助信息。</li>

<li>這個 <code class="docutils literal notranslate">--help</code> 選項可以簡短的表示成 <code class="docutils literal notranslate">-h</code> , 這是唯一一個選項我們不用去指明的（意即，沒有必要在這個參數後加上任何數值）。如果指定其他參數給他會造成錯誤。也因為這樣，我們得到了一個免費的信息。</li>

</ul>

</div>

<h2>介紹位置參數<a class="headerlink" href="#introducing-positional-arguments" title="本標題的永久連結">¶</a></h2>

例子：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("echo")

args = parser.parse_args()

print(args.echo)

</pre></div>

</div>

運行這段代碼：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py

usage: prog.py [-h] echo

prog.py: error: the following arguments are required: echo

$ python3 prog.py --help

usage: prog.py [-h] echo

positional arguments:

echo

optional arguments:

-h, --help show this help message and exit

$ python3 prog.py foo

foo

</pre></div>

</div>

接者是發生的情況：

<li>我們增加了 <code class="xref py py-meth docutils literal notranslate">add_argument()</code> ，利用這個方法可以指名讓我們的程式接受哪些命令列參數。</li>

<li>現在呼叫我們的程序時需要指定一個參數選項。</li>

<li>在這個例子中， <code class="xref py py-meth docutils literal notranslate">parse_args()</code> 這個方法確實根據了 <code class="docutils literal notranslate">echo</code> 這個選項回傳了資料。</li>

<li>The variable is some form of 『magic』 that <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> performs for free

(i.e. no need to specify which variable that value is stored in).

You will also notice that its name matches the string argument given

to the method, <code class="docutils literal notranslate">echo</code>.</li>

</ul>

注意, 雖然 help 秀出了看起來不錯的信息, 但現在並沒有給予到實質幫助。像剛剛增加的 <code class="docutils literal notranslate">echo</code> 這個位置參數，除了猜測和讀原始碼之外，我們根本不曉得該怎麼使用他。因此我們來做一點事讓他變得更有用：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("echo", help="echo the string you use here")

args = parser.parse_args()

print(args.echo)

</pre></div>

</div>

然後我們得到：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 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

</pre></div>

</div>

現在來做一些更有用處的事情：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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)

</pre></div>

</div>

下面是運行這些代碼的結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4

Traceback (most recent call last):

File "prog.py", line 5, in <module>

print(args.square**2)

TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'

</pre></div>

</div>

那並沒有如預期這樣。這是因為 <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> 將我們給予選項的值當成字串，除然我們告訴他要怎麼做。所以我們來告訴 <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> 將這個輸入值當成整數來使用：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

type=int)

args = parser.parse_args()

</pre></div>

</div>

下面是運行這些代碼的結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4

16

$ python3 prog.py four

usage: prog.py [-h] square

prog.py: error: argument square: invalid int value: 'four'

</pre></div>

</div>

這樣很順利。現在程序在開始之前會因為錯誤的輸入而回報有用的訊息並結束掉。

</div>

<h2>介紹選項參數<a class="headerlink" href="#introducing-optional-arguments" title="本標題的永久連結">¶</a></h2>

So far we have been playing with positional arguments. Let us

have a look on how to add optional ones:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("--verbosity", help="increase output verbosity")

args = parser.parse_args()

if args.verbosity:

print("verbosity turned on")

</pre></div>

</div>

接者是結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py --verbosity 1

verbosity turned on

$ python3 prog.py

$ python3 prog.py --help

usage: prog.py [-h] [--verbosity VERBOSITY]

optional arguments:

-h, --help show this help message and exit

--verbosity VERBOSITY

increase output verbosity

$ python3 prog.py --verbosity

usage: prog.py [-h] [--verbosity VERBOSITY]

prog.py: error: argument --verbosity: expected one argument

</pre></div>

</div>

接者是發生的情況：

<li>這個程式是寫成如果有指名 <code class="docutils literal notranslate">--verbosity</code> 這個參數選項那才顯示些資訊，反之亦然。</li>

<li>To show that the option is actually optional, there is no error when running

the program without it. Note that by default, if an optional argument isn’t

used, the relevant variable, in this case <code class="xref py py-attr docutils literal notranslate">args.verbosity</code>, is

given <code class="docutils literal notranslate">None</code> as a value, which is the reason it fails the truth

test of the <a class="reference internal" href="../reference/compound_stmts.html#if"><code class="xref std std-keyword docutils literal notranslate">if</code></a> statement.</li>

<li>Help 訊息稍微有些不一樣。</li>

<li>當使用 <code class="docutils literal notranslate">--verbosity</code> 參數選項時必須要指定一個數值。</li>

</ul>

在上面的例子中 <code class="docutils literal notranslate">--verbosity</code>，接受任意的整數，但對我們的程式來說只接受兩個輸入值， <code class="docutils literal notranslate">True</code> 或 <code class="docutils literal notranslate">False</code>。所以我們來修改一下程式碼使其符合：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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")

</pre></div>

</div>

接者是結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py --verbose

verbosity turned on

$ python3 prog.py --verbose 1

usage: prog.py [-h] [--verbose]

prog.py: error: unrecognized arguments: 1

$ python3 prog.py --help

usage: prog.py [-h] [--verbose]

optional arguments:

-h, --help show this help message and exit

--verbose increase output verbosity

</pre></div>

</div>

接者是發生的情況：

<li>The option is now more of a flag than something that requires a value.

We even changed the name of the option to match that idea.

Note that we now specify a new keyword, <code class="docutils literal notranslate">action</code>, and give it the value

<code class="docutils literal notranslate">"store_true"</code>. This means that, if the option is specified,

assign the value <code class="docutils literal notranslate">True</code> to <code class="xref py py-data docutils literal notranslate">args.verbose</code>.

Not specifying it implies <code class="docutils literal notranslate">False</code>.</li>

<li>It complains when you specify a value, in true spirit of what flags

actually are.</li>

<li>注意不同的 help 文件。</li>

</ul>

<h3>Short options<a class="headerlink" href="#short-options" title="本標題的永久連結">¶</a></h3>

如果你很熟悉命令列的使用的話，你將會發現我還沒講到關於短參數。其實這很簡單：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

action="store_true")

args = parser.parse_args()

if args.verbose:

print("verbosity turned on")

</pre></div>

</div>

And here goes:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py -v

verbosity turned on

$ python3 prog.py --help

usage: prog.py [-h] [-v]

optional arguments:

-h, --help show this help message and exit

-v, --verbose increase output verbosity

</pre></div>

</div>

注意新的表示對於幫助文件也是一樣的

</div>

<h2>現在結合位置與選項參數<a class="headerlink" href="#combining-positional-and-optional-arguments" title="本標題的永久連結">¶</a></h2>

我們的程式成長的越來越複雜：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("square", type=int,

help="display a square of a given number")

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)

</pre></div>

</div>

然後現在的輸出結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py

usage: prog.py [-h] [-v] square

prog.py: error: the following arguments are required: square

$ python3 prog.py 4

16

$ python3 prog.py 4 --verbose

the square of 4 equals 16

$ python3 prog.py --verbose 4

the square of 4 equals 16

</pre></div>

</div>

<li>We’ve brought back a positional argument, hence the complaint.</li>

<li>注意現在的順序對於程式來說已經不再重要了.</li>

</ul>

How about we give this program of ours back the ability to have

multiple verbosity values, and actually get to use them:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("square", type=int,

help="display a square of a given number")

help="increase output verbosity")

args = parser.parse_args()

answer = args.square**2

if args.verbosity == 2:

elif args.verbosity == 1:

print("{}^2 == {}".format(args.square, answer))

else:

print(answer)

</pre></div>

</div>

接者是結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4

16

$ python3 prog.py 4 -v

usage: prog.py [-h] [-v VERBOSITY] square

prog.py: error: argument -v/--verbosity: expected one argument

$ python3 prog.py 4 -v 1

4^2 == 16

$ python3 prog.py 4 -v 2

the square of 4 equals 16

$ python3 prog.py 4 -v 3

16

</pre></div>

</div>

These all look good except the last one, which exposes a bug in our program.

Let’s fix it by restricting the values the <code class="docutils literal notranslate">--verbosity</code> option can accept:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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:

elif args.verbosity == 1:

else:

print(answer)

</pre></div>

</div>

接者是結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 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)

$ python3 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

</pre></div>

</div>

Note that the change also reflects both in the error message as well as the

help string.

Now, let’s use a different approach of playing with verbosity, which is pretty

common. It also matches the way the CPython executable handles its own

verbosity argument (check the output of <code class="docutils literal notranslate">python --help</code>):

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("square", type=int,

help="display the square of a given number")

help="increase output verbosity")

args = parser.parse_args()

answer = args.square**2

if args.verbosity == 2:

elif args.verbosity == 1:

else:

print(answer)

</pre></div>

</div>

我們已經介紹過另一個操作「count」用來計算指定的選項參數出現的次數。

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4

16

$ python3 prog.py 4 -v

4^2 == 16

$ python3 prog.py 4 -vv

the square of 4 equals 16

$ python3 prog.py 4 --verbosity --verbosity

the square of 4 equals 16

$ python3 prog.py 4 -v 1

usage: prog.py [-h] [-v] square

prog.py: error: unrecognized arguments: 1

$ python3 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

$ python3 prog.py 4 -vvv

16

</pre></div>

</div>

<li>Yes, it’s now more of a flag (similar to <code class="docutils literal notranslate">action="store_true"</code>) in the

previous version of our script. That should explain the complaint.</li>

<li>It also behaves similar to 「store_true」 action.</li>

<li>現在來秀一下「count」這個動作會給予什麼。你可能之前就有見過這種用法。</li>

<li>And if you don’t specify the <code class="docutils literal notranslate">-v</code> flag, that flag is considered to have

<code class="docutils literal notranslate">None</code> value.</li>

<li>應該要如預期那樣，就算給予長選項我們也要獲得一樣的輸出結果。</li>

<li>Sadly, our help output isn’t very informative on the new ability our script

has acquired, but that can always be fixed by improving the documentation for

our script (e.g. via the <code class="docutils literal notranslate">help</code> keyword argument).</li>

<li>That last output exposes a bug in our program.</li>

</ul>

讓我們來解決問題

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("square", type=int,

help="display a square of a given number")

help="increase output verbosity")

args = parser.parse_args()

answer = args.square**2

# bugfix: replace == with >=

if args.verbosity >= 2:

elif args.verbosity >= 1:

else:

print(answer)

</pre></div>

</div>

而這也正是它給的：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4 -vvv

the square of 4 equals 16

$ python3 prog.py 4 -vvvv

the square of 4 equals 16

$ python3 prog.py 4

Traceback (most recent call last):

File "prog.py", line 11, in <module>

if args.verbosity >= 2:

TypeError: '>=' not supported between instances of 'NoneType' and 'int'

</pre></div>

</div>

<li>First output went well, and fixes the bug we had before.

That is, we want any value >= 2 to be as verbose as possible.</li>

<li>第三個輸出不是這麼的好。</li>

</ul>

我們來修復這個錯誤：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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:

elif args.verbosity >= 1:

else:

print(answer)

</pre></div>

</div>

We’ve just introduced yet another keyword, <code class="docutils literal notranslate">default</code>.

We’ve set it to <code class="docutils literal notranslate">0</code> in order to make it comparable to the other int values.

Remember that by default,

if an optional argument isn’t specified,

it gets the <code class="docutils literal notranslate">None</code> value, and that cannot be compared to an int value

(hence the <a class="reference internal" href="../library/exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> exception).

而且

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4

16

</pre></div>

</div>

You can go quite far just with what we’ve learned so far,

and we have only scratched the surface.

The <a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> module is very powerful,

and we’ll explore a bit more of it before we end this tutorial.

</div>

<h2>Getting a little more advanced<a class="headerlink" href="#getting-a-little-more-advanced" title="本標題的永久連結">¶</a></h2>

如果我們想要擴展我們的小程式做比範例更多的事：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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("{} to the power {} equals {}".format(args.x, args.y, answer))

elif args.verbosity >= 1:

print("{}^{} == {}".format(args.x, args.y, answer))

else:

print(answer)

</pre></div>

</div>

結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py

usage: prog.py [-h] [-v] x y

prog.py: error: the following arguments are required: x, y

$ python3 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

$ python3 prog.py 4 2 -v

4^2 == 16

</pre></div>

</div>

Notice that so far we’ve been using verbosity level to change the text

that gets displayed. The following example instead uses verbosity level

to display more text instead:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser()

parser.add_argument("-v", "--verbosity", action="count", default=0)

args = parser.parse_args()

if args.verbosity >= 2:

print("Running '{}'".format(__file__))

if args.verbosity >= 1:

print("{}^{} == ".format(args.x, args.y), end="")

print(answer)

</pre></div>

</div>

結果：

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4 2

16

$ python3 prog.py 4 2 -v

4^2 == 16

$ python3 prog.py 4 2 -vv

Running 'prog.py'

4^2 == 16

</pre></div>

</div>

<h3>Conflicting options<a class="headerlink" href="#conflicting-options" title="本標題的永久連結">¶</a></h3>

So far, we have been working with two methods of an

<a class="reference internal" href="../library/argparse.html#argparse.ArgumentParser" title="argparse.ArgumentParser"><code class="xref py py-class docutils literal notranslate">argparse.ArgumentParser</code></a> instance. Let’s introduce a third one,

<code class="xref py py-meth docutils literal notranslate">add_mutually_exclusive_group()</code>. It allows for us to specify options that

conflict with each other. Let’s also change the rest of the program so that

the new functionality makes more sense:

we’ll introduce the <code class="docutils literal notranslate">--quiet</code> option,

which will be the opposite of the <code class="docutils literal notranslate">--verbose</code> one:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>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")

args = parser.parse_args()

if args.quiet:

print(answer)

elif args.verbose:

else:

</pre></div>

</div>

Our program is now simpler, and we’ve lost some functionality for the sake of

demonstration. Anyways, here’s the output:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 prog.py 4 2

4^2 == 16

$ python3 prog.py 4 2 -q

16

$ python3 prog.py 4 2 -v

4 to the power 2 equals 16

$ python3 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

$ python3 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

</pre></div>

</div>

That should be easy to follow. I’ve added that last output so you can see the

sort of flexibility you get, i.e. mixing long form options with short form

ones.

在我們結論之前，你可能想告訴你的用戶這個程式的主要目的，以防萬一他們不知道：

<div class="highlight-python3 notranslate"><div class="highlight"><pre>import argparse

parser = argparse.ArgumentParser(description="calculate X to the power of Y")

group = parser.add_mutually_exclusive_group()

args = parser.parse_args()

if args.quiet:

print(answer)

elif args.verbose:

else:

</pre></div>

</div>

Note that slight difference in the usage text. Note the <code class="docutils literal notranslate">[-v | -q]</code>,

which tells us that we can either use <code class="docutils literal notranslate">-v</code> or <code class="docutils literal notranslate">-q</code>,

but not both at the same time:

<div class="highlight-shell-session notranslate"><div class="highlight"><pre>$ python3 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

</pre></div>

</div>

<a class="reference internal" href="../library/argparse.html#module-argparse" title="argparse: Command-line option and argument parsing library."><code class="xref py py-mod docutils literal notranslate">argparse</code></a> 模組提供了比這裡展示更多的功能。它的文件是非常全面詳細且充滿了例子。通過本教學，你應該比較容易消化它們了。

</div>

<ul>

<li><a class="reference internal" href="#">Argparse 教學</a><ul>

<li><a class="reference internal" href="#introducing-positional-arguments">介紹位置參數</a></li>

<li><a class="reference internal" href="#introducing-optional-arguments">介紹選項參數</a><ul>

<li><a class="reference internal" href="#short-options">Short options</a></li>

</ul>

</li>

<li><a class="reference internal" href="#combining-positional-and-optional-arguments">現在結合位置與選項參數</a></li>

<li><a class="reference internal" href="#getting-a-little-more-advanced">Getting a little more advanced</a><ul>

<li><a class="reference internal" href="#conflicting-options">Conflicting options</a></li>

</ul>

</li>

</ul>

</li>

</ul>

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