Pandas read csv file with float values results in weird rounding and decimal digits

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Pandas uses a dedicated dec 2 bin converter that compromises accuracy in preference to speed.

Passing float_precision='round_trip' to read_csv fixes this.

Check out this page for more detail on this.

After processing your data, if you want to save it back in a csv file, you can pass
float_format = "%.nf" to the corresponding method.

A full exemple:

import pandas as pd

df_in  = pd.read_csv(source_file, float_precision='round_trip')
df_out = ... # some processing of df_in
df_out.to_csv(target_file, float_format="%.3f") # for 3 decimal places

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