Calling function inside another function returns unexpected value while calling first function directly returns expected value

Question

I have written multiple functions that when I call them directly, they result as expected. This is the function:

def number_generator():
    for number in range(1, 815+1):
        file = open('numbers.txt', 'a')
        file.write(f'{number}\n')
        file.close()

It writes numbers from 1 to 815 without problem.

But when I call this function inside another function, it returns unexpected value. This is the other function:

def test():
    file1 = open('file1.txt', 'a')
    file1.write(f'{query_generator()}{number_generator()}\'\n')
    file1.close()

The current result is NoneNone'.

query_generator generates 815 times one SQL query in 815 lines, and number_generator generates number for ID of each my website products.

But when I use them inside test function I do not get the expected value.

What I did so far is I removed the lines related to file variable related to number_generator and query_generator, and added a return statement inside both of them but that did not work.

My expected value is like something below:

UPDATE `tblpricing` SET `msetupfee` = '1'
UPDATE `tblpricing` SET `msetupfee` = '2'
UPDATE `tblpricing` SET `msetupfee` = '3'

How may I reach it?

gmdev · Accepted Answer · 2020-10-20 11:10:29Z

You're passing a function that doesn't return anything into an f string. You noted that you added a return statement, but I am just going to assume that it was just a return followed by nothing else, seeing that that still didn't work. See this simple demo:

def add(a, b):
    result = a+b
    return

a = 1
b = 4
print(f'{a} + {b} is {add(a, b)}')

Output:

1 + 4 is None

Why? Because there is no return value in add(). If we changeadd() to:

def add(a, b):
    result = a+b
    return result

The output is:

1 + 4 is 5

You have not shown what your query_generator() function looks like so without seeing that function, we cannot say if there is another issue than just a missing return value. This line is your culprit:

file1.write(f'{query_generator()}{number_generator()}\'\n')

number_generator() doesn't return anything, it just opens a file and writes the numbers 1 to 815. To solve your issue, create two functions: one for writing the file and one for reading it. I suggest implementing with open() instead of just open(). Also, your current number_generator() opens a file, writes one line, and closes that file 815 times which you probably don't want. Do this instead:

def number_generator():
    with open('numbers.txt', 'w') as file:
        for number in range(1, 816):
            file.write(f'{number}\n')

def get_numbers():
    with open('numbers.txt', 'r') as file:
        lines = [line.strip() for line in file]
        return lines

def query_generator():
    # logic for query generator here

def get_queries():
    # get queries
    # IMPORTANT: Return queries as a list

Note that in get_queries(), the return type should be a list. This is so you can easily iterate and compare both the queries and the numbers simultaneously. Your function could then look like this:

def test():
    # write queries and numbers
    query_generator()
    number_generator()

    # read queries and numbers
    queries = get_queries()
    numbers = get_numbers()

    # zip queries and numbers
    lines = zip(queries, numbers)

    # open file and write each line
    with open('file1.txt', 'w') as file:
        for line in lines:
            comp_line = f'{line[0]} = {line[1]}\n'
            file.write(comp_line)

This gets you your desired output:

UPDATE `tblpricing` SET `msetupfee` = '1'
UPDATE `tblpricing` SET `msetupfee` = '2'
UPDATE `tblpricing` SET `msetupfee` = '3'
...

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