Dates which can be confused in different date format (DD/MM and MM/DD) even if week day is specified

mirror-dates.py

#!/usr/bin/env python3

month_names = [
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December",
]

months = [
    31,
    28,
    31,
    30,
    31,
    30,
    31,
    31,
    30,
    31,
    30,
    31,
]

months_leap = [
    31,
    29,
    31,
    30,
    31,
    30,
    31,
    31,
    30,
    31,
    30,
    31,
]

def build_date_to_num(months):
    return dict(
        ((mon, day), num) for num, (mon, day) in enumerate(
            (mon, day) for mon, count in enumerate(months) for day in range(count)
        )
    )

date_to_num = build_date_to_num(months)
date_to_num_leap = build_date_to_num(months_leap)

def week_collisions(months, date_to_num):
    for mon, count in enumerate(months):
        for day in range(mon):
            my_num = date_to_num[(mon, day)]
            other_num = date_to_num[(day, mon)]
            if (my_num - other_num) % 7 == 0:
                yield mon, day

def format_pair(mon, day):
    return "\t%s %d <=> %s %d" % (month_names[day], mon + 1, month_names[mon], day + 1)

def main():
    print("non-leap year:")
    for mon, day in week_collisions(months, date_to_num):
        print(format_pair(mon, day))
    print("leap year:")
    for mon, day in week_collisions(months_leap, date_to_num_leap):
        print(format_pair(mon, day))

if __name__ == '__main__':
    main()

output.txt

non-leap year:
	January 7 <=> July 1
	February 8 <=> August 2
	May 9 <=> September 5
	January 11 <=> November 1
	July 11 <=> November 7
	March 12 <=> December 3
leap year:
	February 3 <=> March 2
	January 6 <=> June 1
	May 9 <=> September 5
	July 11 <=> November 7
	February 12 <=> December 2
	March 12 <=> December 3