What is the difference between using squared brackets or dot to access a column?

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The “dot notation”, i.e. df.col2 is the attribute access that’s exposed as a convenience.

You may access an index on a Series, column on a DataFrame, and an item on a Panel directly as an attribute:

df['col2'] does the same: it returns a pd.Series of the column.

A few caveats about attribute access:

  • you cannot add a column (df.new_col = x won’t work, worse: it will silently actually create a new attribute rather than a column – think monkey-patching here)
  • it won’t work if you have spaces in the column name or if the column name is an integer.

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