In the following examples, I am splitting an empty string by a space. However, in the first example I explicitly used a space and in the second example, I didn't. My understanding was that .split() and .split(' ') were equivalent.

Why do these two examples give different outputs?

In [1]: "".split(' ')
Out[1]: ['']In [2]: "".split()
Out[2]: []

From the python's documentation -

If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns [].

Sep is the separator. What it says is if we don't pass anything to split, whitespaces are considered as separators, it will apply a different algorithm to split strings and will return us a [] but since you passed a sep, it will not apply this algorithm