Stop the for loop and just get true or false

Question

I make this example code for my problem. I need to get out just True or False and stop the loop but i dont know how?

def test():
    list = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"
    for x in list:
        if user==x:
            print True
        else:
            print False
test()

The output:

False
False
True
False
False
False

score 5 · Answer 1 · edited May 23 '17 at 12:27

5

You can just use in:

def test():
    users = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"
    return user in users

Demo:

>>> users = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
>>> user = u"jean"
>>> user in users
True

Note that list is not a good variable name since it shadows built-in list.

In case you need a for loop, you need to break the loop when you hit a match and print False in the else block of the for loop:

def test():
    users = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"
    for x in users:
        if user == x:
            print True
            break
    else:
        print False

edited May 23 '17 at 12:27

Community

1
1

answered Jul 21 '14 at 01:28

alecxe

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no i should use for loop in my code. this is just example for my problem.i need solution for `for loop` – yuyb0y Jul 21 '14 at 01:30
I try to put `break` but the output print `True` then print `False` but i need when find the correct value print `True` and stop. – yuyb0y Jul 21 '14 at 01:37
@yuyb0y make sure you run the same code as in the answer - I've tested it before posting. – alecxe Jul 21 '14 at 01:38
While this is the correct usage, I find the Python syntax for `else` with `for` and `while` loops particularly unintuitive. I wish they had used another keyword instead. – Peter Gibson Jul 21 '14 at 01:56
@PeterGibson yeah, it is not a popular programming technique, but it is good to have it in a toolkit. – alecxe Jul 21 '14 at 02:00

score 2 · Answer 2 · answered Jul 21 '14 at 01:41

2

While alecxe has the best answer, there's one more option: variables!

def test():
    users = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"

    found = False
    for x in users:
        if user == x:
            found = True;

    print found

answered Jul 21 '14 at 01:41

Bill Lynch

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I think this is clearer than using the `else` statement with a loop – Peter Gibson Jul 21 '14 at 02:00

score -1 · Answer 3 · answered Jul 21 '14 at 01:51

-1

def test():
    list = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"
    for x in list:
        if user==x:
            print True
            break
        else:
            print False
test()

You can use break to exit a loop prematurely.

answered Jul 21 '14 at 01:51

Will

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3

Note that this will print `"False False True"`. – Bill Lynch Jul 21 '14 at 01:58

score -1 · Answer 4 · answered Jul 21 '14 at 04:07

-1

def test():
    list = [u"sam", u"jay", u"jean", u"smo", u"gon", u"bil"]
    user = u"jean"
    for x in list:
        if user==x:
            print True
            return # or return True depending on how you want it to work
                   # break might also be of value here
        else:
            print False
test()

answered Jul 21 '14 at 04:07

BWStearns

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Note that this will print `"False False True"`, and it is __identical__ to Will's answer from 3 hours before you. – Bill Lynch Jul 21 '14 at 15:58
Sorry. Had it open got busy and didn't hit send for a while. – BWStearns Jul 21 '14 at 18:06

Stop the for loop and just get true or false

4 Answers4