Python 2中的无限While循环

Question

file = open(r'd:\holiday_list.txt', 'w')
date = ''
while(date != '0'):
    date = input('\nEnter Date (YYYYMMDD) : ')
    date = date[:4] + '-' + date[4:6] + '-' + date[5:]
    file.write(date)
print('Job Done!')
file.close()

This program is supposed to take dates (eg:20112016) as input and write it to a file. The problem is the program does not exit the while loop. If i enter a 0, it prompts me to enter another date.

Answer 1

You have your check in the wrong place: you manipulate the date as soon as you read it in, and the result is no longer '0' when you get back to the top of the loop. Try this:

date = input('\nEnter Date (YYYYMMDD) : ')
while(date != '0'):
    date = date[:4] + '-' + date[4:6] + '-' + date[5:]
    file.write(date)
    date = input('\nEnter Date (YYYYMMDD) : ')

ANother check is the most basic of debugging: put in a print command to show exactly what you read in. Perhaps something like

print("date is ||", date"||")

The vertical bars will show any leading or trailing white space, such as the newline character. (Get rid of that with the strip method.)

Answer 2

An alternative solution to Prune's is to use an if statement with a break :

    while(True):
        date=input('\nEnter Date (YYYYMMDD) : ')
        if(date=='0'):
            break
        ...#your work here

This way you don't have to have an additional input outside the loop.