How to Serialize a Dictionary to a Query String in Python

Convert a Python dictionary into a URL-encoded query string using the standard library's urllib.parse.urlencode function.

Easy Python 3.9+ Aug 9, 2026 Dictionaries & sets 14 views 0 copies

urllib query-string urlencode serialization dictionary

Python code

14 lines

Python 3.9+

import urllib.parse

def dict_to_query_string(params):
    """Serialize a dictionary to a URL query string."""
    return urllib.parse.urlencode(params)

if __name__ == "__main__":
    data = {
        "name": "Alice Johnson",
        "age": 30,
        "city": "New York",
        "interests": ["coding", "hiking"]
    }
    print(dict_to_query_string(data))

Output

stdout

name=Alice+Johnson&age=30&city=New+York&interests=%5B%27coding%27%2C+%27hiking%27%5D

How it works

The urllib.parse.urlencode function accepts a dictionary and returns a string with key-value pairs joined by &, URL-encoding both keys and values. Spaces become +, and special characters are percent-encoded automatically. The function handles multiple values for the same key if the dictionary's values are lists or tuples, but here the list is treated as a single value. This is the standard library approach, no third-party packages needed.

Common mistakes

Expecting list values to be serialized as repeated keys; urlencode treats them as a single value unless doseq=True is used.
Forgetting to handle non-string values; urlencode converts them to strings automatically.
Assuming the output uses %20 for spaces instead of +.
Using json.dumps instead of urlencode, which produces a JSON string, not a valid query string.

Variations

Use urlencode(data, doseq=True) to turn list values into repeated parameters like interests=coding&interests=hiking.
Pass a list of tuples instead of a dict to preserve order and allow duplicates.

Real-world use cases

Building query strings for HTTP GET requests to REST APIs, ensuring parameters are properly URL-encoded.
Constructing analytics tracking URLs with campaign parameters passed as a dictionary.
Creating signed URLs with query parameters for generating shareable links or pagination tokens.

How to Serialize a Dictionary to a Query String in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Dictionaries & sets

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