Parse numbers and lists from config files with configparser

Question

I'm doing a relatively big project for my final thesis and therefore I am using a .ini file for storing and retrieving settings. However, I am unable to find an elegant solution for how to convert the strings (well, actually the strings inside the dictionary) that Configparser returns to numbers (ints and floats) and/or lists.

Googling the issue, I came across this SO thread which only tackles the 'list' part of my problem but using the top rated solution (defining lists inside the .ini file like that: list=item1,item2) didn't do anything for me, as the 'list' still shows up as a string after parsing. Also, I do not want to change format.

So I decided I would try it myself and came up with this solution:

import configparser # create a new instance of a 'ConfigParser' class config = configparser.ConfigParser() # create mock-content for the config file config["Test"] = { "test_string":"string", "test_int":"2", "test_float":"3.0", "test_list":"item1, item2" } # get the relevant settings settings = config["Test"] # pack the relevant settings into a dictionary settings = dict(settings) # iterate through all the key-value pairs and convert them, if possible for key, value in settings.items(): # try to convert to int try: settings[key] = int(value) # if the value can't be converted to int, it might be a float or a list except ValueError: # try converting it to a float try: settings[key] = float(value) # if the value can't be converted to float, try converting to list except ValueError: if "," in value: cont = value.split(",") settings[key] = [item.strip() for item in cont] else: settings[key] = value print(type(settings["test_string"])) print(settings)

However, this seems so very inelegant and is so heavily nested and the task itself seems so important that I cannot believe that there is no "more official" solution to this that I am simply unable to find.

So, could please someone help me out here and tell me if there really is no better, more straightforward way to achieve this!?

Jarvis · Accepted Answer · 2020-12-29 18:31:58Z

2

Best I can do is this (though it's kinda hacky and probably dangerous too):

for key, value in settings.items(): try: # will handle both ints and floats, even tuples with ints/floats settings[key] = eval(value) except NameError: # this means it's a string or a tuple with strings get_val = list(map(str.strip, value.split(","))) settings[key] = get_val if get_val[1:] else get_val[0]

This will work correctly for ints, floats as well as your comma separated values (it will evaluated it as a tuple, I guess that should be fine though I added a condition for that anyway).

edited Dec 29, 2020 at 18:31

answered Dec 29, 2020 at 18:00

Jarvis

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6 Comments

Viggar Over a year ago

Thanks for your solution! I'd upvote it but I don't have the 'reputation' yet... But in what way is your solution dangerous, could you please elaborate? And, since I am writing a software for an experiment on a satellite and stability is key here, would you recommend your solution over mine regarding stability or the other way around?

Viggar Over a year ago

Also, how is it possible that there is no "official" solution for this? I mean it must be an important part of config files to store all kinds of data types or am I doing something wrong here?

Jarvis Over a year ago

Sure, in the try part, the eval basically evaluates your string in an interpreter, so if it's a valid type like int or float, it will pass, it's like when you type 1 or 1.0 in interpreter and you get the same thing back. On the other hand, if you write a string without quotes or with commas, it returns error, hence the except part. Here, it is assumed that the type is string or string with commas, so I split it and return first element (string with no commas split around it will return list of length 1) or the complete list in else case.

Jarvis Over a year ago

By dangerous, I meant using eval which is certainly fine for your case. As to why it is dangerous, you can see this or this.

Viggar Over a year ago

Wow, that is a lot of information. Thank you very much for helping me out! I'm going to think about what kind of types I am going to need and then decide from there. You have a good... whatever it is you are celebrating next ;)

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