write a file after create some random strings

Question

import random
class simulate_DNA:
    def create_DNA(length):
        sequence = ""
        for i in range(length):
            sequence = sequence + random.choice("ATGC")
        return print(sequence)
def main():
    length = 10
    output_file = input("Enter output file path and name: ")
    output_file = open(output_file, "w")
    for i in range(10):
        # simulate_DNA.create_DNA(length)
        output_file.write(simulate_DNA.create_DNA(length))
        output_file.readline()
    output_file.close()
if __name__ == '__main__':
    main()

I got this error after running the code above: TypeError: write() argument must be str, not None Would anyone please tell me how to fix this error? Thank you so much!

Additionally, in the main function, readline() cannot be used if output_file is opened for writing. If you want to read the file change 'w' to 'w+' in open() — Desty, Feb 17 '22 at 01:34
Would you please tell me why return print(sequence) doesn't print a random string? — Chris, Feb 17 '22 at 02:01

score 1 · Answer 1 · answered Feb 17 '22 at 01:32

1

The print function returns None, and you're trying to return the result of the print function => So it's None

Replace this: return print(sequence) By: return sequence

answered Feb 17 '22 at 01:32

PySoL

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Would you please tell me why return print(sequence) doesn't print a random string? – Chris Feb 17 '22 at 01:50
1

The `print(sequence)` does print the random string. But it returns `None` instead of the random string you expected. So this lead to the error at this line `output_file.write(simulate_DNA.create_DNA(length))` because you're trying to do `output_file.write(None)`. This is illegal as file writer only allows the string and integer but None. – PySoL Feb 17 '22 at 02:28
So why does simulate_DNA.create_DNA(length) create None in this case? – Chris Feb 17 '22 at 12:23
1

Because the function `create_DNA` returns `print(...)` which is none. – PySoL Feb 17 '22 at 14:08

write a file after create some random strings

1 Answers1