Day 25: Wrong Use of or in Conditions

 

Day 25: Wrong Use of or in Conditions

This is a classic Python gotcha that trips up beginners and even experienced developers.

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❌ The Mistake

x = 3

if x == 1 or 2: 
    print("x is 1 or 2")

You might expect this to run only when x is 1 or 2…
But it always runs, no matter what x is.

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🤔 Why This Happens

Python reads the condition like this:

if (x == 1) or (2):

• x == 1 → True or False

• 2 → always True (non-zero values are truthy)

So the whole condition is always True.

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✅ The Correct Way

Option 1: Compare explicitly

if x == 1 or x == 2:
  print("x is 1 or 2")

Option 2 (Recommended): Use in

if x in (1, 2): 
    print("x is 1 or 2")

Cleaner, safer, and more Pythonic ✅

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❌ Why the Mistake Is Dangerous

• Conditions behave incorrectly

• Bugs are hard to notice

• Logic silently fails

• Leads to unexpected program flow

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🧠 Simple Rule to Remember

✔ or does not repeat comparisons
✔ Use in for multiple equality checks
✔ If it reads like English, it’s probably wrong 😄

# Think like Python, not English
if x in (1, 2): 
   ...

🐍 Pro tip: When checking multiple values, in is almost always the best choice.