Why replace treats an integer value 999 as 999.0?

[snippsat]

So in Python, I don't need to do that explicitly and as long as two numbers (could both be float/double or one float/double and one integer) are close, they are considered to be the same?

Has to be very close if remove one 0 and it's False.

>>> 3 == 3.000000000000001
False

For better control on how close look at math.isclose() numpy also have numpy.isclose.
There also a decimal module where can better control over precision,
can eg do financial calculation or as a calculator would output.

>>> 0.1 * 3
0.30000000000000004

>>> from decimal import Decimal
>>> 
>>> result = Decimal('0.1') * Decimal('3')
>>> result
Decimal('0.3')
>>> print(result)
0.3

Pandas is a own big beast and can have other rules