Syntax
square = lambda x: x * x print(square(5)) # 25
Equivalent to:
def square(x):
return x * x
Where Lambdas Shine
pairs = [("a", 3), ("b", 1), ("c", 2)]
pairs.sort(key=lambda p: p[1])
# [('b',1), ('c',2), ('a',3)]
nums = [1, 2, 3, 4, 5] evens = list(filter(lambda n: n % 2 == 0, nums)) squared = list(map(lambda n: n*n, nums))
When to Avoid Lambdas
- More than one expression → use
def. - Needs a docstring or type hint → use
def. - Used in multiple places → define and name it.
💡 For HKDSE, stick to
def unless the question explicitly shows lambda syntax. Lambdas are rarely required but often useful in data-processing tasks.Practise this on PyForm — free
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