Please help i learned how to make some math functions but i want to learn how to make file functions 😟

Question

in python we have the math functions ( working with some variables and some numbers 😑 ) but can I make a function for a file like a program that rewrites a chosen file I tried but I don't how I will make this function understand that let's say☺
def my_function(x,y):
if x > y
print("x")
else:
print("y")

so can I make a function with a file like

def file_rewrite(filename.txt):
open("filename.txt","w")
file.write("hi")
file.close()

print(file_rewrite(hello.txt))
open("hello.txt","r")
note:hello.txt exists

Answer 1

@Gordie thanks for replying but how can I choose the file extension

Answer 2

@Gordie does that mean the file extension is not important cause it's the same file name and the important thing is the opening method ( mode )