if as a ternary operator python

Question

I'm trying to take this function (which runs):

def shift_on_character(string, char):
    final = list(string)
    a = [i for index, i in enumerate(string) if i.lower() == char.lower()]
    for i in range(0,len(string)):
        if string[i] != a[0]:
            final.append(string[i])
            final.pop(0)
        else: break
    print(final)
shift_on_character("zipfian", "f")

And simplify it as much as possible. Specifically, I'm trying to use a ternary operator on the if statement to shorten that section to one line of code. I want to write:

def shift_on_character(string, char):
    final = list(string)
    a = [i for index, i in enumerate(string) if i.lower() == char.lower()]
    for i in range(0,len(string)):
        final.append(string[i]) & final.pop(0) if string[i] != a[0] else break
   print(final)
shift_on_character("zipfian", "f")

But I keep getting some random syntax error when simplifying the if statement. If I make a simpler action for the "true" condition case or if I take the else off then I still get an error which implies that python is having trouble with the "if" condition.

What's happening and how can I fix it?

Thanks!

You cannot use break with the ternary operator.

donkopotamus
– donkopotamus

2016-01-22 00:43:45 +00:00
Commented Jan 22, 2016 at 0:43 — donkopotamus
– donkopotamus, Commented Jan 22, 2016 at 0:43

donkopotamus · Accepted Answer · 2016-01-22 00:59:03Z

1

You cannot use break with the ternary operator. If I understand your function (which rotates around the first instance of char it finds), then why not implement simply as:

def shift_on_character(string, char):
    try:
        pos = string.index(char)
        return string[pos:] + string[:pos]
    except IndexError:
        # what do you want to do if char is not in string??
        return string

answered Jan 22, 2016 at 0:59

donkopotamus

23.4k3 gold badges58 silver badges61 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Erin Wolpert Over a year ago

Thanks for your help!

Hugh Bothwell · Accepted Answer · 2016-01-22 01:03:57Z

1

It would be simpler (and quite a bit faster) to use Python's built-in functions:

def shift_on_character(string, char):
    try:
        index = string.lower().index(char.lower())
        string = string[index:] + string[:index]
    except ValueError:
        pass
    return list(string)

answered Jan 22, 2016 at 1:03

Hugh Bothwell

57k9 gold badges91 silver badges103 bronze badges

Comments

Leif Andersen · Accepted Answer · 2016-01-22 00:59:44Z

0

Your problem is using break as a part of the ternary if. If you really want to use a ternary if, you can do it like this:

def shift_on_character(string, char):
    final = list(string)
    a = [i for index, i in enumerate(string) if i.lower() == char.lower()]
    for i in range(0,len(string)):
        if string[i] == a[0]: break
        final.append(string[i]) or final.pop(0) if string[i] != a[0] else False
    print(final)
shift_on_character("zipfian", "f")

This works because you aren't really using the result of the expression and are just relying on it's side effects. In general this really isn't a good practice and I would just keep the original expression you had before.

edited Jan 22, 2016 at 0:59

answered Jan 22, 2016 at 0:48

Leif Andersen

22.4k21 gold badges75 silver badges109 bronze badges

2 Comments

Erin Wolpert Over a year ago

this solution gives a type error (TypeError: unsupported operand type(s) for &: 'NoneType' and 'str')

Leif Andersen Over a year ago

Yeah, I realized I had left the & in there, and changed it to an or, which works with None types. Still, @donkopotamus's solution is much better.

Collectives™ on Stack Overflow

if as a ternary operator python

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related