How to make a dictionary (dict) from separate lists of keys and values in Python ?

To create a dictionary from two separate lists of keys and values in Python, you can use the built-in zip() function combined with the dict() constructor. Here’s a step-by-step guide:

Method 1: Using zip() and dict()

keys = ["a", "b", "c"]
values = [1, 2, 3]

# Combine the lists into key-value pairs
my_dict = dict(zip(keys, values))

print(my_dict)
# Output: {'a': 1, 'b': 2, 'c': 3}

Method 2: Using a Dictionary Comprehension

keys = ["name", "age", "city"]
values = ["Alice", 30, "New York"]

my_dict = {k: v for k, v in zip(keys, values)}
print(my_dict)
# Output: {'name': 'Alice', 'age': 30, 'city': 'New York'}

Handling Edge Cases

1. Unequal List Lengths:
   zip() truncates to the shortest list. To avoid missing data, ensure lists are of equal length:

   if len(keys) == len(values):
       my_dict = dict(zip(keys, values))
   else:
       print("Error: Lists are unequal in length.")

2. Duplicate Keys:
   The last occurrence of a duplicate key will overwrite previous ones:

   keys = ["a", "a", "b"]
   values = [1, 2, 3]
   print(dict(zip(keys, values)))  # Output: {'a': 2, 'b': 3}

Alternative: Loop Explicitly

keys = ["x", "y", "z"]
values = [10, 20, 30]
my_dict = {}

for k, v in zip(keys, values):
    my_dict[k] = v

print(my_dict)  # Output: {'x': 10, 'y': 20, 'z': 30}

Summary

Approach	Use Case
dict(zip(keys, values))	Most concise and efficient method
Dictionary Comprehension	Flexibility (e.g., add conditions)
Explicit Loop	For custom logic during iteration

Use zip() + dict() for simplicity and readability in most scenarios.