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Table of Contents
1. Basic method: Generate dictionary from list
2. Create indexed dictionary using enumerate
3. Merge two lists to generate dictionary
4. Dictionary derivation (a more concise way)
Home Backend Development Python Tutorial Python for loop to create a dictionary

Python for loop to create a dictionary

Jul 13, 2025 am 01:56 AM
python dictionary

There are the following methods to create dictionaries using Python's for loop: 1. The basic method is to first define an empty dictionary and add key-value pairs to the loop, such as initializing the name list to 0 points; 2. Use enumerate to generate an indexed dictionary, such as corresponding fruit to its index; 3. When merging two lists to construct a dictionary, the keys and values are one by one through the index; 4. The dictionary derivation provides a more concise writing method, the logic remains unchanged but the form is compact. These methods are suitable for different data structure scenarios, so as to ensure that the key value source is clear.

Python for loop to create a dictionary

Creating dictionaries using Python's for loop is actually a very common operation, especially when dealing with data conversion or batch-constructing key-value pairs. The key is understanding how to dynamically add keys and values to the dictionary in a loop.

Python for loop to create a dictionary

1. Basic method: Generate dictionary from list

If you have a set of data and want to build a dictionary through a loop, the most common way is to define an empty dictionary first and then gradually add key-value pairs in the loop.

For example, you want to use a set of names as keys and set the initial score to 0:

Python for loop to create a dictionary
 names = ['Alice', 'Bob', 'Charlie']
scores = {}

for name in names:
    scores[name] = 0

This way you can get:

 {'Alice': 0, 'Bob': 0, 'Charlie': 0}

This method is suitable for scenarios with small data volume and simple structure.

Python for loop to create a dictionary

2. Create indexed dictionary using enumerate

Sometimes you want the dictionary keys or values to contain index information, such as corresponding elements in the list to their positions, you can use enumerate .

 fruits = ['apple', 'banana', 'cherry']
fruit_dict = {}

for index, fruit in enumerate(fruits):
    fruit_dict[fruit] = index

The result is:

 {'apple': 0, 'banana': 1, 'cherry': 2}

This writing method is useful when processing data that needs to be recorded in sequence or numbered, such as numbering options, creating mapping tables, etc.

3. Merge two lists to generate dictionary

If you have two lists, one is a key and the other is a value, and they correspond one by one, you can also use a for loop to construct a dictionary.

 keys = ['name', 'age', 'city']
values = ['Tom', 25, 'New York']

person = {}
for i in range(len(keys)):
    person[keys[i]] = values[i]

Final result:

 {'name': 'Tom', 'age': 25, 'city': 'New York'}

It should be noted here that the lengths of the two lists must be the same, otherwise data misalignment or omission may occur.

4. Dictionary derivation (a more concise way)

Although the title talks about using for loops, it is worth mentioning that there is a more concise way to write in Python - dictionary derivation, which is essentially abbreviation of for loops.

For example, the above example can be written as:

 names = ['Alice', 'Bob', 'Charlie']
scores = {name: 0 for name in names}

Or the case where two lists are merged:

 keys = ['name', 'age', 'city']
values = ['Tom', 25, 'New York']
person = {keys[i]: values[i] for i in range(len(keys))}

The logic is the same, but the writing method is more compact, suitable for writing method that you like to do in one line.


Basically that's it. The key point in creating a dictionary with a for loop is to figure out where the keys and values come from, and how to correctly combine them into the dictionary in the loop. Whether it is traversing one list or using two lists in conjunction, as long as the structure is clear, it will not be difficult to achieve.

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