def defined_value(df, col1, col2, col3):
    for row in df.itertuples():
        col1 = 'Col1'
        result = row.col1 + row.col2 + row.col3
        if result > 10:
            return str('Result > 10: ', result)

df.loc[:, 'test_1'] = defined_value(df, 'Col1', 'Col2', 'Col2')

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-27-a0908c223773> in <module>()
----> 1 df.loc[:, 'test_1'] = defined_value(df, 'Col1', 'Col2', 'Col2')

<ipython-input-26-6194bd333695> in defined_value(df, col1, col2, col3)
      2     for row in df.itertuples():
      3         col1 = 'Col1'
----> 4         result = row.col1 + row.col2 + row.col3
      5         if result > 10:
      6             return str('Result > 10: ', result)

AttributeError: 'Pandas' object has no attribute 'col1'