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Python / Core Python Fundamentals Interview Questions

Can you create a tuple comprehension in Python, and what is a generator expression?

There is no tuple comprehension syntax in Python — (x for x in range(5)) is a generator expression, not a tuple. To get a tuple from a comprehension-like construct, wrap a generator expression in tuple():

# Generator expression — lazy, single-pass, no tuple
gen = (x**2 for x in range(5))
print(type(gen))    # 

# Tuple from a generator expression
t = tuple(x**2 for x in range(5))
print(t)            # (0, 1, 4, 9, 16)
print(type(t))      # 

# List comprehension — eager, stored in memory
lst = [x**2 for x in range(5)]

# Generator expression used inline — no intermediate list
total = sum(x**2 for x in range(1_000_000))  # memory-efficient

Generator expressions are the memory-friendly alternative to list comprehensions when you only need to iterate once or pass the result to a function that accepts an iterable (like sum(), max(), sorted(), list()). They are lazy — values are generated on demand.

When should you prefer a generator expression over a list comprehension?

  • The sequence will be consumed once, not indexed or iterated multiple times.
  • The sequence is large and you cannot afford to materialise it all in memory.
  • You are passing it directly to an aggregation function (sum, any, all).

Nested generator expressions are possible but hard to read — more than one level of nesting is usually a sign to extract a helper function.

What type does (x**2 for x in range(5)) produce?
Why is sum(x**2 for x in range(1_000_000)) more memory-efficient than sum([x**2 for x in range(1_000_000)])?

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