Can a paper be rejected for only detailing an algorithm mathematically and not programmatically (via pseudocode)? Imagine you are a peer reviewer presented with a paper that states an algorithm was implemented in python to test an analytical process on large datasets. The details of how the algorithmic process are detailed extensively via mathematical denotation and formulas, but no actual pseudocode or programming examples are shown. Would you consider the paper to be incomplete, or would the mathematical examples suffice (provided they are robust enough and don't withhold any information whatsoever)?
In theoretical computer science (I cannot speak for other fields) it is very common not to give pseudocode, but only a high-level description of the algorithm. Your paper should always explain your ideas as clearly as possible, and as an author it is your job to select the most suitable presentation. This does not necessarily need to be pseudocode. Painstakingly presenting every little implementation detail may not add much to the paper and instead distract the reader. If you think foregoing pseudocode results in a better paper, by all means do so (unless the journal you are submitting to specifically requires it).
If your paper presents an implementation in Python, I would expect the source code to be publicly available somewhere and referenced in the paper.