An argparse argument can be limited to specific values with the [`choices`][1] parameter:

    ...
    parser.add_argument(&#39;--val&#39;,
                        choices=[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;],
                        help=&#39;Special testing value&#39;)
    
    args = parser.parse_args(sys.argv[1:])

See the [docs][1] for more details.


  [1]: https://docs.python.org/library/argparse.html#choices

I&#39;m working on some custom UIView-based input controls, and I&#39;m trying to ascertain proper practice for setting up the view. When working with a UIViewController, it&#39;s fairly simple to use the `loadView` and related `viewWill`, `viewDid` methods, but when subclassing a UIView, the closest methosds I have are ``awakeFromNib`, `drawRect`, and `layoutSubviews`. (I&#39;m thinking in terms of setup and teardown callbacks.) In my case, I&#39;m setting up my frame and internal views in `layoutSubviews`, but I&#39;m not seeing anything onscreen. 

What is the best way to ensure that my view has the correct height and width that I want it to have? (My question applies regardless of if I&#39;m using autolayout, although there might be two answers.) What&#39;s the proper &quot;best practice&quot;?


Proper practice for subclassing UIView?

I have `Set&lt;String&gt; result` &amp; would like to convert it to comma separated string. My approach would be as shown below, but looking for other opinion as well.

    List&lt;String&gt; slist = new ArrayList&lt;String&gt; (result);
    StringBuilder rString = new StringBuilder();
    
    Separator sep = new Separator(&quot;, &quot;);
    //String sep = &quot;, &quot;;
    for (String each : slist) {
        rString.append(sep).append(each);
    }
    
    return rString;



Best way to convert list to comma separated string in java

Is it possible to require that an [`argparse`][1] argument be one of a few preset values?

My current approach would be to examine the argument manually and if it&#39;s not one of the allowed values call [`print_help()`][2] and exit.

Here&#39;s the current implementation:

    ...
    parser.add_argument(&#39;--val&#39;,
                        help=&#39;Special testing value&#39;)
    
    args = parser.parse_args(sys.argv[1:])
    if args.val not in [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]:
        parser.print_help()
        sys.exit(1)

It&#39;s not that this is particularly difficult, but rather that it appears to be messy.


  [1]: https://docs.python.org/library/argparse.html
  [2]: https://docs.python.org/library/argparse.html#argparse.ArgumentParser.print_help

Allowing specific values for an Argparse argument

Is it possible to require that an <a href="https://docs.python.org/library/argparse.html" target="_blank" rel="noopener noreferrer"><code>argparse</code></a> argument be one of a few preset values?
My current approach would be to examine the argument manually and if it's not one of the allowed values call <a href="https://docs.python.org/library/argparse.html#argparse.ArgumentParser.print_help" target="_blank" rel="noopener noreferrer"><code>print_help()</code></a> and exit.
Here's the current implementation:
<pre><code class="hljs language-css">...
parser.add_argument('--val',
 help='Special testing value')

args = parser.parse_args(sys.argv[1:])
if args.val not in ['a', 'b', 'c']:
 parser.print_help()
 sys.exit(1)
</code></pre>
It's not that this is particularly difficult, but rather that it appears to be messy.

I&#39;m working on an AI portion of a guessing game. I want the AI to select a random letter from this list. I&#39;m doing it as a set so I can easily remove letters from the list as they are guessed in the game and are therefore no longer available to be guessed again.

it says `set` object isn&#39;t indexable. How can I work around this?

    import random 
    aiTurn=True
    
    while aiTurn == True:
        allLetters = set(list(&#39;abcdefghijklmnopqrstuvwxyz&#39;))
        aiGuess=random.choice(allLetters)
        
        
     
        print (aiGuess) 

random.choice from set? python

When I draw a shape using:

    canvas.create_rectangle(10, 10, 50, 50, color=&quot;green&quot;)

Does Tkinter keep track of the fact that it was created? 

In a simple game I&#39;m making, my code has one `Frame` create a bunch of rectangles, and then draw a big black rectangle to clear the screen, and then draw another set of updated rectangles, and so on. 

Am I creating thousands of rectangle objects in memory? 

I know you can assign the code above to a variable, but if I don&#39;t do that and just draw directly to the canvas, does it stay in memory, or does it just draw the pixels, like in the HTML5 canvas?

How to clear Tkinter Canvas?

I understand that &quot;.pyc&quot; files are compiled versions of the plain-text &quot;.py&quot; files, created at runtime to make programs run faster. However I have observed a few things:

1. Upon modification of &quot;py&quot; files, program behavior changes. This indicates that the &quot;py&quot; files are compiled or at least go though some sort of hashing process or compare time stamps in order to tell whether or not they should be re-compiled.
2. Upon deleting all &quot;.pyc&quot; files (`rm *.pyc`) sometimes program behavior will change. Which would indicate that they are not being compiled on update of &quot;.py&quot;s.

Questions:

* How do they decide when to be compiled?
* Is there a way to ensure that they have stricter checking during development?


When are .pyc files refreshed?

I am trying to print the last part of a string before a certain character.  

I&#39;m not quite sure whether to use the string .split() method or string slicing or maybe something else.    

Here is some code that doesn&#39;t work but I think shows the logic:  

    x = &#39;http://test.com/lalala-134&#39;
    print x[&#39;-&#39;:0] # beginning at the end of the string, return everything before &#39;-&#39;

Note that the number at the end will vary in size so I can&#39;t set an exact count from the end of the string.  

 


how to get the last part of a string before a certain character?

In python 3 I can make arguments and return type annotations. Example:

    class Graph:
        def __init__(self, V: int, E: int, edges: list):
            pass
    
        @classmethod
        def fromfile(cls, readobj: type(sys.stdin)):
            pass
    
        def V(self) -&gt; int:
            pass
    
        def E(self) -&gt; int:
            pass

The problem is I can&#39;t make an annotation with return type of the current class (Graph), which is not defined yet.
Example:

    class Graph:
       def reverse(self) -&gt; Graph:
           pass

This code goes with error

    def reverse(self) -&gt; Graph:
    NameError: name &#39;Graph&#39; is not defined

These annotations are really useful both for documenting and allowing IDE to recognize argument and return types =&gt; enable autocomplete

UPD:
So what I came up is this is either impossible or requires some hacks I don&#39;t like, so I decided to use just `def reverse (self) -&gt; &#39;Graph&#39;:` 
which is understandable for documentation although breaks the rule. The downside is that it doesn&#39;t work for IDE autocomplete.

putting current class as return type annotation

Is there a way to make argparse recognize anything between two quotes as a single argument? It seems to keep seeing the dashes and assuming that it&#39;s the start of a new option


I have something like:

    mainparser = argparse.ArgumentParser()
    subparsers = mainparser.add_subparsers(dest=&#39;subcommand&#39;)
    parser = subparsers.add_parser(&#39;queue&#39;)
    parser.add_argument(&#39;-env&#39;, &#39;--extraEnvVars&#39;, type=str,
                            help=&#39;String of extra arguments to be passed to model.&#39;)
    ...other arguments added to parser...

But when I run:

    python Application.py queue -env &quot;-s WHATEVER -e COOL STUFF&quot;

It gives me:

    Application.py queue: error: argument -env/--extraEnvVars: expected one argument

If I leave off the first dash, it works totally fine, but it&#39;s kind of crucial that I be able to pass in a string with dashes in it. I&#39;ve tried escaping it with \ , which causes it to succeed but adds the \ to the argument string Does anyone know how to get around this? This happens whether or not -s is an argument in parser.

EDIT: I&#39;m using Python 2.7.

EDIT2: 

    python Application.py -env &quot; -env&quot;

works perfectly fine, but

    python Application.py -env &quot;-env&quot;

does not.

EDIT3: Looks like this is actually a bug that&#39;s being debated already: http://www.gossamer-threads.com/lists/python/bugs/89529, http://python.6.x6.nabble.com/issue9334-argparse-does-not-accept-options-taking-arguments-beginning-with-dash-regression-from-optp-td578790.html. It&#39;s only in 2.7 and not in optparse. 

EDIT4: The current open bug report is: http://bugs.python.org/issue9334


Can&#39;t get argparse to read quoted string with dashes in it?

I&#39;ve been searching through a lot of the subparser examples on here and in general but can&#39;t seem to figure this seemingly simple thing out.

I have two var types of which one has constraints so thought subparser was the way to go. e.g. -t allows for either &quot;A&quot; or &quot;B&quot;. If the user passes &quot;A&quot; then they are further required to also specify if it is either &quot;a1&quot; or &quot;a2&quot;. If they pass just &quot;B&quot; then nothing.

Can I do this and have argparse return me what type of &quot;A&quot; was passed or if it was just &quot;B&quot;?

The below seems to work but for some reason breaks when passing anything after the subparse.

e.g. from a linux terminal

    &gt;&gt; python test01.py -t A a1 -v 61

errors with...

    usage: test01.py a1 [-h]
    test01.py a1: error: unrecognized arguments: -v

Hopefully that makes sense.

The code:

    import argparse
    
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(help=&#39;types of A&#39;)
    
    parser.add_argument(&quot;-t&quot;,
                        choices = [&quot;A&quot;, &quot;B&quot;],
                        dest = &quot;type&quot;,
                        required=True,
                        action=&#39;store&#39;,
                        help=&quot;Some help blah blah&quot;)
    
    cam_parser = subparsers.add_parser(&#39;a1&#39;, help=&#39;Default&#39;)
    cam_parser.set_defaults(which=&#39;a1&#39;)
    
    cam_parser = subparsers.add_parser(&#39;a2&#39;, help=&#39;parse this instead of default&#39;)
    cam_parser.set_defaults(which=&#39;a2&#39;)
    
    
    parser.add_argument(&quot;-v&quot;,
                        nargs = &#39;+&#39;,
                        required=True,
                        dest = &quot;version&quot;,
                        type=int,
                        action=&#39;store&#39;,
                        help=&quot;some version help blah blah&quot;)   
    
    argument = parser.parse_args()
    
    print argument.type
    print argument.version

How to use argparse subparsers correctly?

When I run `parsePlotSens.py -s bw hehe`, it says that `hehe` is an unrecognized argument. However, if I run `parsePlotSens.py hehe -s bw`, it&#39;s OK. Ideally, I would like it work for both cases. 

Any tips? The following is my code:

    if __name__ == &#39;__main__&#39; :

        parser = argparse.ArgumentParser(prog=&#39;parsePlotSens&#39;);
        parser.add_argument(&#39;-s&#39;, &#39;--sort&#39;, nargs =1, action = &#39;store&#39;, choices = [&#39;mcs&#39;, &#39;bw&#39;], default=&#39;mcs&#39;, help=sorthelp)
        parser.add_argument(&#39;filename&#39;, nargs =&#39;+&#39;, action = &#39;store&#39;)
        option = parser.parse_args(sys.argv)

python argparse: unrecognized arguments

What I need is:

    pro [-a xxx | [-b yyy -c zzz]]

I tried this but does not work. Could someone help me out?

    group= parser.add_argument_group(&#39;Model 2&#39;)
    group_ex = group.add_mutually_exclusive_group()
    group_ex.add_argument(&quot;-a&quot;, type=str, action = &quot;store&quot;, default = &quot;&quot;, help=&quot;test&quot;)
    group_ex_2 = group_ex.add_argument_group(&quot;option 2&quot;)
    group_ex_2.add_argument(&quot;-b&quot;, type=str, action = &quot;store&quot;, default = &quot;&quot;, help=&quot;test&quot;)
    group_ex_2.add_argument(&quot;-c&quot;, type=str, action = &quot;store&quot;, default = &quot;&quot;, help=&quot;test&quot;)

Thanks!

Python argparse mutual exclusive group

Using python and argparse, the user could input a file name with -d as the flag.

    parser.add_argument(&quot;-d&quot;, &quot;--dmp&quot;, default=None)

However, this failed when the path included spaces. E.g. 

    -d C:\SMTHNG\Name with spaces\MORE\file.csv

NOTE: the spaces would cause an error (flag only takes in &#39;C:SMTHNG\Name&#39; as input).

    error: unrecognized arguments: with spaces\MORE\file.csv

Took me longer than it should have to find the solution to this problem...
(did not find a Q&amp;A for it so I&#39;m making my own post)

Content Type	Original Author	Original Content on Stackoverflow
Question	Moshe	View Question on Stackoverflow
Solution 1 - Python	Moshe	View Answer on Stackoverflow

Allowing specific values for an Argparse argument

Python Problem Overview

Python Solutions

Solution 1 - Python

Best way to convert list to comma separated string in java

Proper practice for subclassing UIView?

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