Interactively selecting items from a list

Question

I have a need to print the contents of a folder to a user, who then picks one of the files. The program then takes that choice and uses it elsewhere.

My code to achieve this:

keylist = os.listdir('./SomeFolder/')
keycount = len(keylist)
for key in keylist:
    keynum = (keylist.index(key) + 1)
    print(str(keynum) + ' : ' + str(key))
while True:
    try:
        keychoice = int(input('Please Choose a Key : '))
        print()
        if 1 <= keychoice <= keycount:
            break
        else:
            raise MenuError()
    except ValueError:
        print('Please enter a valid option')
        continue
    except MenuError:
        print('Please enter a valid option, ' + str(keychoice) + " isn't an option.")
        continue

chosenkey = keylist[(keychoice - 1)]
print(chosenkey + ' has been chosen')

Overall, this works ok. But, is there a better way to do it?

I'm new to python, so any pointers are greatly received. The program in which i use this is pySignare Thanks.

Answer 1

I'll take a closer look at this shortly, but the thing that jumped out at me was this:

for key in keylist:
    keynum = (keylist.index(key) + 1)
    print(str(keynum) + ' : ' + str(key))

You're using list.index to get do a lookup of a key while you're iterating through it. Don't do that.

The old better way of doing that was this:

for i in range(len(keylist)):
    key = keylist[i]
    keynum = i
    print("{} : {}".format(keynum,key))

The REAL way you should do this is:

for keynum, key in enumerate(keylist):
    print("{} : {}".format(keynum + 1,key))

enumerate(iterable) runs through iterable and returns a tuple for each item, representing (index, value) . You're unpacking those with keynum, key . In order to fit what you did originally, you add one to keynum before displaying it, then you'll subtract one again from the user input.

I would also make a function that defines integer input. Something like:

def int_input(prompt,range_=None):
    while True:
        in_ = input(prompt)
        try: in_ = int(in_)
        except ValueError: pass
        else:
            if not range or if in_ in list(range_): return in_
        print("Invalid value, please try again.")

This will let you do something like:

keylist = os.listdir("path/to/dir")
for i,key in enumerate(keylist):
    print("{} : {}".format(keynum+1, key))
chosen_key = int_input("Which dir? ",range(1,len(keylist)+1)) - 1
print ("{} has been chosen!".format(keylist[chosen_key]))

Answer 2

The only improvement I can offer is to use the enumerate() function :

keylist = os.listdir('./SomeFolder/')
keycount = len(keylist)

for keynum, key in enumerate(keylist, 1):
    print('{} : {}'.format(keynum, key))

I started the count for you at 1 to match your output; users find counting from 1 more natural anyway.

This also makes use of string formatting , a much more readable and concise method of building strings.

Answer 3

The two main things you do here that are worth avoiding are the while True loop and the lack of functions. In general as well, I think you can accomplish what you are looking for much easier:

def getChoice(path):
    file_list = os.listdir(path)
    for i,j in enumerate(file_list):
        print "{choice}: {f}".format(choice=i+1, f=j) #Index from one.
    user_choice = int(input("What file do you wish to use?"))

    if user_choice in range(len(file_list)):
        print "You chose {f}".format(f=file_list[user_choice - 1])
        return file_list[user_choice-1]
    else:
        print "That is not a valid selection."
        return False

Then I'd wrap the function call so I had something like:

choice = False
while not choice:
    choice = getChoice(path)

This way you avoid a while true loop, and your getChoice function is independently testable of anything else.

Note: I didn't test this code, but it looks good.