Python Asserts

All of these assume basic use of the assert keyword:

assert <condition>, "<optional error message>"

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✅ Python Assert — 20 Basic Assignments

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1) Simple Assert

Write:

assert 5 > 2

Run and ensure no error is thrown.

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2) Failing Assert

Write an assert that fails:

assert 2 > 5, "2 is not greater than 5"

Observe the AssertionError.

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3) Assert on Even Number

Ask the user for a number and assert that it’s even.

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4) Assert on Positive

Input a number from the user and assert that it’s positive.

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5) Assert in Function

Write a function check_positive(n) that asserts n >= 0.

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6) Assert String Length

Ask the user for a string and assert its length is ≥ 5.

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7) Assert List Non-Empty

Create a list from user input and assert it’s not empty.

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8) Assert Integer Input

Ask user for input, convert to int, and assert conversion succeeds (use try/except to loop until valid).

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9) Assert Alphabet String

Ask user for a word and assert it contains only letters (str.isalpha()).

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10) Assert Range 1–10

Ask user for a number and assert it’s between 1 and 10.

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11) Assert True/False

Create a variable flag = True and assert that it’s True.

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12) Assert on List Length

Given a list, assert its length is exactly 3.

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13) Assert Sum

Given:

nums = [1,2,3]

Assert that sum(nums) == 6.

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14) Assert Dictionary Key

Create a dict and assert a specific key exists:

d = {"name":"Alice"}

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15) Assert Function Return

Write a function square(x) that returns x*x, then assert:

square(5) == 25

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16) Assert No Zero Division

Ask two numbers and assert the second is not 0 before dividing.

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17) Assert Float

Ask user input and assert it is a float value (use try/except + assert).

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18) Assert Unique List

Ask user for 5 numbers and assert the list has no duplicates.

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19) Assert File Exists

Ask user for a filename and assert that it exists on disk.

(Hint: use import os and os.path.exists())

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20) Assert Valid Email

Ask user for a string and assert it contains '@' and '.'.

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🧠 What You’re Practicing

Concept	Example
Basic assert	assert x > 0
Assert with message	assert cond, "error info"
Using assert in functions	check inputs
Validating user input	simple input guards
Combining assert + try/except	safe validation

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📌 Example Starter Code

Positive Number with Assert

n = int(input("Enter a positive number: "))
assert n >= 0, "Number must be positive"
print("Valid input:", n)

Even Number Using Assert

x = int(input("Enter a number: "))
assert x % 2 == 0, "Number must be even!"
print("Even number OK!")

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⚠️ Important Notes

✔ An assert will raise an AssertionError if the condition fails. ✔ Use clear messages to indicate why the assertion failed.

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