pandas to_json ignoring microseconds

September 19, 2023

When writing a pandas dataframe to file using to_json, the microseconds seem lost, with only the milliseconds preserved:

import pandas as pd
from datetime import datetime as dt

df = pd.DataFrame( { 'timestamp' : [dt.strptime('2023-09-19 10:10:10.111222', '%Y-%m-%d %H:%M:%S.%f')] } )
print(df)
df.to_json('data.json')
df1 = pd.read_json('data.json')
print(df1)

giving output:

                   timestamp
0 2023-09-19 10:10:10.111222
                timestamp
0 2023-09-19 10:10:10.111

How can I preserve the microseconds?

>Solution :

By default, pandas.DataFrame.to_json() uses milliseconds as the date unit. You can change the precision with the date_unit argument. The options are ‘s’, ‘ms’, ‘us’, ‘ns’ for second, millisecond, microsecond, and nanosecond respectively.

For your example, change the line writing the data frame to json to:
df.to_json('data.json', date_unit='us')