BUG: User-facing AssertionError in Series.to_timestamp

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample, a copy-pastable example

In [5]: import pandas as pd

In [6]: pd.Series([0]).to_timestamp()
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-6-1a9d08d7daba> in <module>
----> 1 pd.Series([0]).to_timestamp()

~/sandbox/pandas/pandas/core/series.py in to_timestamp(self, freq, how, copy)
   4565             new_values = new_values.copy()
   4566
-> 4567         assert isinstance(self.index, (ABCDatetimeIndex, ABCPeriodIndex))
   4568         new_index = self.index.to_timestamp(freq=freq, how=how)
   4569         return self._constructor(new_values, index=new_index).__finalize__(

AssertionError:

Problem description

Users shouldn’t see AssertionErrors like this, since they may be disabled when the interpreter starts up.

Expected Output

We probably want this to be a TypeError.

[TomAugspurger]

Not sure. I would hope that with

if not isinstance(self.index (ABCDatetimeIndex, ABCPeriodIndex)):
    raise TypeError(...)

# hopefully mypy knows the types here

but we can make the assert for mypy after we’ve done the user-facing check if needed.

[simonjayhawkins]

• I have confirmed this bug exists on the latest version of pandas.

the assertion was added in #31126 (i…e not yet released)

on 1.0.3

>>> import pandas as pd
>>>
>>> pd.__version__
'1.0.3'
>>>
>>> pd.Series([0]).to_timestamp()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\simon\pandas\pandas\core\series.py", line 4529, in to_timestamp
    new_index = self.index.to_timestamp(freq=freq, how=how)
AttributeError: 'RangeIndex' object has no attribute 'to_timestamp'
>>>