How do I check if a directory exists and then, if so, ask for a new directory name in Python?

Question

So first off I'm a complete newb at Python so sorry if my code is horrible. This is just for a proof of concept, the actual code doesn't really matter, just the function.

So I'm trying to create a directory by specifying a name for it. I want the program to check if a directory with that name already exists and if it does, ask for a new name and create that directory. The checking bit works fine, but when it loops around to ask for a different name it seems to be storing the original one (the duplicate), which then overwrites the new name when it gets returned. This means I keep getting the old directory name returned instead of the new one (hope that makes sense?)

def casefile():
    print '\n\nPlease enter a case name/reference: '
    case_name = raw_input()
    if not os.path.exists('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name)):
        os.mkdir('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name))
        print '\n{} case file created. All logs will be saved to C:\Users\laura17\Documents\ProgrammeOutput\{}' \
            .format(case_name, case_name)
    else:
        print '\n**Case already exists. Please choose a different case name.**'
        casefile()
    return case_name

As an example, I printed out case_name just before the return function to see what was happening:

def casefile():
    print '\n\nPlease enter a case name/reference: '
    case_name = raw_input()
    if not os.path.exists('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name)):
        os.mkdir('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name))
        print '\n{} case file created. All logs will be saved to C:\Users\laura17\Documents\ProgrammeOutput\{}' \
            .format(case_name, case_name)
    else:
        print '\n**Case already exists. Please choose a different case name.**'
        casefile()
    print case_name
    return case_name

And this was the output:

Any help would be much appreciated. Thank you.

Answer 1

Problem

When you are calling the function recursively, you are not returning from the previously called function.

What happens is, when you call the casefile first time and enter an existing name ie Case1 , an entry is created in the stack for it. Lets call it casefile{1}. At the line casefile() in the else statement, the function will be called recursively.

Now, due to this recursive call, another entry for the function is created in the stack. Lets call this casefile{2}. Now the controlled would be passed to this function, but note that casefile{1} has not yet run its course - you have not returned from it.

So now the control is at casefile{2}. This time you enter a non-existing name ie Case2 . The casefile{2} does not go to the else branch and thus no more recursive calls would be made. So not it prints the name just like you asked it to (which in the scope of casefile{2} happens to be Case2 , and returns the name.

But now the control goes back to casefile{1}, which will now exit the else statement and run the next line: print case_name , which for the scope of casefile{1} happens to be Case1 . So it prints it and returns.

Solution

You should return after calling the function recursively. Please change the code to this:

def casefile():
    print '\n\nPlease enter a case name/reference: '
    case_name = raw_input()
    if not os.path.exists('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name)):
        os.mkdir('C:\\Users\\laura17\\Documents\\ProgrammeOutput\\{}'.format(case_name))
        print '\n{} case file created. All logs will be saved to C:\Users\laura17\Documents\ProgrammeOutput\{}' \
            .format(case_name, case_name)
    else:
        print '\n**Case already exists. Please choose a different case name.**'
        return casefile()
    print case_name
    return case_name

Please note that i have changed the line casefile() in the else statement to return casefile() .

This would only print/return the name being passed to it by its recursively called functions.

Hope this helps. Cheers!

Answer 2

What your code goes into recursion hence it returns both names. The following code first tries to make directory with the given name, if it cannot it will ask for another input till it is able to create one. Finally, it returns the name of the directory which is created. For python 2 please use raw_input() and for python 3, input().

Hope this helps!

import os

def casefile(path):
    while(True):
        try :
            # raw_input() for python 2
            case_name = input("Enter the case: ") # for python 3
            os.makedirs(path+case_name)
            return (case_name)
        except:
            pass

Open this to see output of my terminal

Answer 3

Use os.makedirs to create directory, use try except to catch any error.

In [11]: import os

In [12]: try:
    ...:     os.makedirs('/Users/abc/projects')
    ...: except OSError:
    ...:     print('Already exists')
    ...: else:
    ...:     print('Directory created')
    ...:
Already exists