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ryanharris.dev
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Using ternaries for variable assignment in Python

One of my favorite "tricks" as a programmer is to condense conditional logic (i.e. if/else blocks) into one line when assigning variables. The ternary operator makes this possible.

If you come from a JavaScript background like I do, you may have seen this done before with a question mark.

const isSuccess = data.response ? true : false
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Essentially, this means if data.response is defined we should assign isSuccess the value of true. Otherwise, we'll set it to false.

Recently, I used a ternary operation in Python for the first time. While it, ultimately, works the same way I found the slight difference between languages interesting.

To recreate the snippet above in Python, we could write:

is_success = True if data.response else False
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In this case, the right-side of the assignment leads with the "truthy" value, as opposed to the value we're checking. It's not a big difference, but worth noting the difference in API.

The ? operator has a special place in my heart because I've used it so much. However, Python's ternary operator syntax is probably easier to read for beginners.

Top comments (4)

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jonrandy profile image
Jon Randy 🎖️

Not really the greatest example. As JS has the concept of truthiness and falsiness, then writing:

const isSuccess = data.response ? true : false
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is effectively the same as writing:

const isSuccess = data.response // actually making isSuccess kinda redundant
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unless you have a very solid reason for requiring a boolean (perhaps to include as part of a JSON request/response) - in which case you could just use:

const isSuccess = !!data.repsonse
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ryanharris profile image
ryanharris.dev

Fair point. For the purposes of demonstration I was "keeping it simple", but you're technically correct. Thanks for calling it out.

Personally, I'm not a huge fan of the !! because I think it is harder to grok than its alternatives.

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ryanharris profile image
ryanharris.dev

Didn't mean to suggest it was invented in JavaScript. My background is in JavaScript, so I was just drawing a parallel to my previous use of the conditional operator.