How to Write JSON in Pandas: Syntax and Examples

You can write JSON from a pandas DataFrame using the to_json() method. This method converts the DataFrame into a JSON string or directly writes it to a file by specifying a file path.

Syntax

The basic syntax to write JSON from a pandas DataFrame is:

• DataFrame.to_json(path_or_buf=None, orient='columns', lines=False)

Where:

• path_or_buf: file path or buffer to write JSON to. If None, returns JSON string.
• orient: format of JSON string. Common options are 'columns', 'records', 'index'.
• lines: if True, writes JSON as newline-delimited records.

python

df.to_json(path_or_buf=None, orient='columns', lines=False)

Example

This example shows how to create a DataFrame and write it to a JSON file with different orientations.

python

import pandas as pd

# Create a sample DataFrame
data = {'name': ['Alice', 'Bob'], 'age': [25, 30], 'city': ['NY', 'LA']}
df = pd.DataFrame(data)

# Write DataFrame to JSON file with default orientation (columns)
df.to_json('output_columns.json')

# Write DataFrame to JSON file with records orientation (list of dicts)
df.to_json('output_records.json', orient='records')

# Write DataFrame to JSON file with lines=True (newline delimited JSON)
df.to_json('output_lines.json', orient='records', lines=True)

# Read back one file to show output
with open('output_records.json', 'r') as f:
    json_content = f.read()

print(json_content)

Output

[{"name":"Alice","age":25,"city":"NY"},{"name":"Bob","age":30,"city":"LA"}]

Common Pitfalls

Common mistakes when writing JSON with pandas include:

• Not specifying orient correctly, which can lead to unexpected JSON structure.
• Forgetting to set lines=True when writing newline-delimited JSON, causing parsing errors in some tools.
• Assuming to_json() writes to a file by default; it returns a string if no file path is given.

python

import pandas as pd

data = {'a': [1, 2], 'b': [3, 4]}
df = pd.DataFrame(data)

# Wrong: expecting file but no path given
json_str = df.to_json()  # returns string, does not write file

# Right: write to file

df.to_json('output.json')

# Wrong: forgetting lines=True for newline JSON
# df.to_json('output_lines.json', orient='records')  # This writes one big JSON array

# Right: use lines=True

df.to_json('output_lines.json', orient='records', lines=True)

Quick Reference

Parameter	Description	Common Values
path_or_buf	File path or buffer to write JSON. If None, returns JSON string.	None or 'filename.json'
orient	Format of JSON output.	'columns', 'records', 'index', 'split', 'values'
lines	Write JSON as newline-delimited records.	True or False

Key Takeaways

Use DataFrame.to_json() to write JSON from pandas.

Specify a file path in to_json() to write directly to a file.

Choose the orient parameter to control JSON structure.

Set lines=True for newline-delimited JSON format.

Without a file path, to_json() returns a JSON string.