Dictionaries & sets
Key–value maps, uniqueness, counting, grouping, and fast lookups.
How to Invert a Dictionary in Python Safely
Swap dictionary keys and values while detecting duplicate values to prevent silent data loss.
def invert_dict_safely(d):
inverted = {}
for key, value in d.items():
if value not in inverted:
inverted[value] = key
else:
raise ValueError(f"Duplicate value '{value}' would cause data loss")
return inverted
if __name__ == "__main__":
sample = {"a": 1, "b": 2,…How to swap dict keys and values in Python when values are unique
Swap dict keys and values using a dict comprehension, with a guard that raises an error when values repeat.
def swap_dict_keys_values(d):
"""Swap keys and values in a dict, assuming values are unique."""
if len(set(d.values())) != len(d.values()):
raise ValueError("Values must be unique to swap keys and values")
return {v: k for k, v in d.items()}
if __name__ == "__main__":
original = {"a": 1, "b": …Browse by section
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Dictionaries & sets — Python code examples
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This page collects dictionaries & sets snippets — short, copy-ready Python you can paste into our free online IDE and run without installing anything. Each sample includes a plain-English explanation and the full source code.
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