How to read a text file using Object-Oriented Programming in Python 3

Question

I am trying to read a text file in Python using a new Class and OOP but I can't find the right way to do it without using imperative programming like this.

def read_operators_file(file_name):
        in_file=open(file_name)
        for i in range(constants.HEADER_TOTAL_LINES):
            in_file.readline()
        operators=[]
        for line in in_file:
            name, nationality, domain, hours, duration = line.strip().split(', ')
            duration=int(duration)
            domain=tuple(domain.strip('(').strip(')').split('; '))
            operators.append((name, nationality, domain, hours, duration))
        in_file.close()
        return operators


def read_requests_file(file_name):
        in_file = open(file_name)
        for i in range(constants.HEADER_TOTAL_LINES):
            in_file.readline()
        requests = []
        for line in in_file:
            name, language, domain, service, duration = line.strip().split(', ')
            duration = int(duration)
            requests.append((name, language, domain, service, duration))
        in_file.close()
        return requests

Thanks,
mikeysantana

You can certainly wrap those functions in a class, but what's the benefit of using a class? Do you need some state to survive between invocations? — tobias_k
– tobias_k, Commented Mar 6, 2018 at 15:22

tobias_k · Accepted Answer · 2018-03-06 15:32:49Z

While you certainly could convert this to an OOP style, I don't think that it would help much. Instead, I'd suggest trying an FP style. You can define another function, taking the different conversion functions as parameters, e.g. str as basically no-operation, int, or a lambda for more complex stuff. Also, you should use with for opening files.

Something like this (not tested):

def read_fields(file_name, functions):
    with open(file_name) as in_file:
        for i in range(constants.HEADER_TOTAL_LINES):
            in_file.readline()
        result = []
        for line in in_file:
            fields = [f(x) for f, x in zip(functions) line.strip().split(', ')]
            result.extend(fields)
        return result

def read_operators_file(file_name):
    f_domain = lambda d: tuple(d.strip('(').strip(')').split('; '))
    # fields:                    name nat  domain    hrs  dur
    return read_fields(file_name, (str, str, f_domain, str, int))

def read_requests_file(file_name):
    # fields:                    name lang domn serv dur
    return read_fields(file_name, (str, str, str, str, int))

Or using a generator function:

def read_fields(file_name, functions):
    with open(file_name) as in_file:
        for i in range(constants.HEADER_TOTAL_LINES):
            in_file.readline()
        for line in in_file:
            yield from (f(x) for f, x in zip(functions) line.strip().split(', '))

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