Why doesn't pandas update a variable's dtype when populating a dataframe?

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February 2019

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I noticed a difference between two pandas version, and was wondering why that was the case / if it was an expected behaviour:

import pandas as pd
df = pd.DataFrame(columns = ("Name", "Age"))
df.loc[1] = "Jane", 5
df.loc[2] = "Riley", 24
df.dtypes

In my test:

  • with Python 3.5 and Pandas 0.18.1, populating the dataframe does update the "object" dtype of the Age variable to "float64"
  • with Python 3.7 and Pandas 0.23.4, populating the dataframe does not update the "object" dtype of the Age variable

Why is that? I couldn't find an explanation in the documentation.

Edit: I just noticed df.infer_objects().dtypes, which might be particularly relevant... Did the automatic "inference" get ditched along the way?

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