Which Python built-in functions are most important to know for coding interviews?

Python's built-in namespace contains roughly 70 functions. The ones that come up constantly in interview problems and real-world code are:

Sequence and iteration: len(), range(), enumerate(), zip(), sorted(), reversed(), min()/max() (accept a key= argument), sum(), map(), filter(), any(), all().

Type conversion: int(), float(), str(), bool(), list(), tuple(), set(), dict().

Object introspection: type(), isinstance(), issubclass(), dir(), vars(), hasattr(), getattr(), setattr().

nums = [3, 1, 4, 1, 5, 9, 2, 6]

print(sorted(nums))               # [1, 1, 2, 3, 4, 5, 6, 9]
print(sorted(nums, reverse=True)) # [9, 6, 5, 4, 3, 2, 1, 1]

words = ['banana', 'apple', 'cherry']
print(sorted(words, key=len))     # ['apple', 'banana', 'cherry']

print(any(x > 8 for x in nums))  # True  (9 > 8)
print(all(x > 0 for x in nums))  # True  (all positive)

# zip — pair two lists
keys   = ['a', 'b', 'c']
values = [1,   2,   3  ]
print(dict(zip(keys, values)))    # {'a':1,'b':2,'c':3}

isinstance(obj, (int, float)) is the right way to check types — it handles subclasses correctly unlike type(obj) == int. For finding the max by a custom criterion: max(employees, key=lambda e: e['salary']).

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