Converting a string into an integer

Question

I am trying to write a program that determines leap years. My problem is that I cannot convert the year variable into an integer. I attempt to parse the variable in the try statement. the error I am receiving is

line 19, in divide_by_4
if (year%4) == 0:
TypeError: not all arguments converted during string formatting

My code is below: and the file I imported in only had 1804 in it

def is_year(year):
 '''determine if the input year can be converted into an integer'''
 try:
 int(year)
 return year
 except ValueError:
 print("current year is not a year")
def divide_by_4(year):
 if (year%4) == 0:
 return True
def divide_by_100(year):
 if (year % 100) == 0:
 return True
def divide_by_400(year):
 if (year % 400) == 0:
 return True
def leap_year(year):
 if is_year(year):
 if divide_by_4(year):
 if divide_by_100(year):
 if divide_by_400(year):
 return True
 else:
 if divide_by_400(year):
 return True
def main():
 input_file = input("Enter the file input file name: ")
 output_file = input("Enter the output file name: ")
 try:
 file_in = open(input_file, 'r')
 except IOError:
 print("The input file could not be opened. The program is ending")
 try:
 file_out = open(output_file, 'w')
 except IOError:
 print("The output file could not be opened. The program is ending")
 for years in file_in:
 if leap_year(years):
 file_out.write(years)
 file_in.close()
 file_out.close()
main() 

Answer 1

How about:

def divide_by_4(year):
 if (int(year) % 4) == 0:
 return True

Justification: In is_year function you don't actually convert String to int. Instead you just check if it is possible to convert it. That's why you need to make actual conversion ( int(year) ) before you use year as integer.

The same problem will occur in divide_by_100.

Answer 2

when you read data from file, the data's type is string , so you can't use year % 4. you can do like that:

def leap_year(year):
 if is_year(year):
 year = int(year)
 ......

then do it