Assigning value to variable when IF statement is false causes error in Python

Question

I'm writing a function in Python that should search a string for a substring, then assign the index of the substring to a variable. And if the substring isn't found, I'd like to assign -1 to the variable to be used as a stop code elsewhere. But I get an error that I don't understand. Here is a simplified version of the code:

test = "abc"
search_str = "z"
index_search_str = test.index(search_str) if search_str in test else index_search_str = -1

If I run this code, the value of index_search_str should be -1, but instead I get this error (using PyCharm):

 index_search_str = test.index(search_str) if search_str in test else index_search_str = -1
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: invalid syntax. Maybe you meant '==' or ':=' instead of '='?

But if I change = -1 to := -1, it still gives an error. What am I missing?

You got your ternary operator wrong. the assignment only happens at the start, not in the "else". Corrected version: index_search_str = test.index(search_str) if search_str in test else -1 — Mike Scotty
– Mike Scotty, Commented Jul 17, 2022 at 0:56
The real question is, why are you not just using index_search_str = test.find(search_str)? — BeRT2me
– BeRT2me, Commented Jul 17, 2022 at 2:45

AlphaCoX · Accepted Answer · 2022-07-17 00:59:59Z

3

I think, in using ternary operator, value should be returned.

test = "azbc"
search_str = "z"
index_search_str = test.index(search_str) if search_str in test else -1

print(index_search_str)    # print value maybe  "1"

answered Jul 17, 2022 at 0:59

AlphaCoX

3772 silver badges10 bronze badges

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

Comments

Ghanteyyy · Accepted Answer · 2022-07-17 02:40:56Z

3

You cannot assign variable in one-line statement

test = "abc"
search_str = "z"
index_search_str = test.index(search_str) if search_str in test else -1

edited Jul 17, 2022 at 2:40

answered Jul 17, 2022 at 0:58

Ghanteyyy

4941 gold badge5 silver badges13 bronze badges

Comments

MikroT · Accepted Answer · 2022-07-17 01:16:44Z

2

Your code have syntax errors.

I think you need something like this:

test = "abc"
search_str = "z"
if search_str in test:
    print("match")
    index_search_str = test.index(search_str)
    print(index_search_str)
else :
    print("not match")
    index_search_str = -1
    print(index_search_str)

"not match"
"-1"

test = "abc"
search_str = "c"
if search_str in test:
    print("match")
    index_search_str = test.index(search_str)
    print(index_search_str)
else :
    print("not match")
    index_search_str = -1
    print(index_search_str)

match
2

edited Jul 17, 2022 at 1:16

answered Jul 17, 2022 at 1:09

MikroT

812 bronze badges

Comments

BeRT2me · Accepted Answer · 2022-07-17 02:49:18Z

1

Just use str.find instead... it does exactly what you're trying to do by default.

>>> test = "abc"
>>> print(test.find('z'))
-1

>>> print(test.find('b'))
1

answered Jul 17, 2022 at 2:49

BeRT2me

13.3k2 gold badges18 silver badges39 bronze badges

Comments

ANIK ISLAM SHOJIB · Accepted Answer · 2022-07-17 00:58:47Z

0

Try

index_search_str = test.index(search_str) if search_str in test else -1

answered Jul 17, 2022 at 0:58

ANIK ISLAM SHOJIB

3,3383 gold badges31 silver badges48 bronze badges

Collectives™ on Stack Overflow

Assigning value to variable when IF statement is false causes error in Python

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related