1) No pattern matching. In 2019, this is just unacceptable. Pattern matching is so fundamental to good FP style that without it, it becomes almost impossible to write good and clean code.
2) Statement vs expression distinction. There’s no need for this and it just crippled the language. Why can’t I use a conditional inside an assignment? Why can’t I nest conditions inside other functions? It makes no sense and is stupid and inelegant.
3) Related to 2), why do I need to use a return statement? Just return the last expression like many other (better) languages
4) Bad and limited data structures. In Python all you get are arrays, hashmaps, sets. And only sets have an immutable version. This is unacceptable. Python claims to be “batteries included” but if you look at the Racket standard library it has like 20x more stuff and it’s all 100x better designed. In Scala you get in the standard library support for Lists, Stacks, Queues, TreeMaps, TreeSets, LinearMaps, LinearSet, Vectors, ListBuffers, etc.
5) Embarrassing performance. Python is so slow it’s shameful. I wrote a compiler and some interpreters in college and I honestly think I could create a similar language 10x faster than Python. Sometimes you need to trade off performance and power, but that’s not even the case with Python: it’s an order of magnitude slower than other interpreted languages (like Racket).
6) Missing or inadequate FP constructs. Why are lambdas different from a normal function? Why are they so crippled? Why do they have a different conditional syntax? The only sort of FP stuff Python has is reduce/filter/map. What about flatMap, scanr, scanl, foldl, foldr? Or why doesn’t Python have flatten? All of these are very useful and common operations and Python just makes everyone write the same code over and over again.
7) No monads. Monads can be used for exceptions, futures, lists, and more. Having to manually write some try catch thing is unseemly and worse than the monadic Haskell or Scala approach.
8) No threads and no real single process concurrency. Despite Python being used a lot, no one really seems to care about it. How can such a problem not be solved after over 20 years? It’s shameful and makes me wonder about the skill of Guido. There’s no reason why Python couldn’t have turned into something beautiful like Racket, but instead it has been held back by this grumpy old guy who is stuck in the past.
9) Others might not have a problem with this, but I detest Python’s anything can happen dynamic typing. It makes reasoning about code difficult and it makes editor introspections almost impossible. If I can’t know the exact type of every variable and the methods attached to it, it hampers my thinking a lot. I use Python for data science and if I could just have a language that was compiled and had static typing I would be 3x as productive.
Let me conclude by saying there currently is one good reason to use Python: if the domain is ML/DL/quant/data science Python is still the undisputed king. The libraries for Python are world class: scipy, sklearn, pandas, cvxpy, pytorch, Kerala, etc.
But Julia is catching up very fast and the people I have talked to are getting ready to ditch Python in 2-3 years for Julia. I don’t think I’ve encountered anyone who didn’t prefer Julia to Python.