## Fix Python – How to split/partition a dataset into training and test datasets for, e.g., cross validation?

What is a good way to split a NumPy array randomly into training and testing/validation dataset? Something similar to the cvpartition or crossvalind functions in Matlab.
….

## Fix Python – Handling very large numbers in Python

I’ve been considering fast poker hand evaluation in Python. It occurred to me that one way to speed the process up would be to represent all the card faces and suits as prime numbers and multiply them together to represent the hands. To whit:
class PokerCard:
faces = ‘23456789TJQKA’
suits = ‘cdhs’
facePrimes = [11, 13, 17, 19, 23, 29, ….

## Fix Python – Why is early return slower than else?

This is a follow-up question to an answer I gave a few days back. Edit: it seems that the OP of that question already used the code I posted to him to ask the same question, but I was unaware of it. Apologies. The answers provided are different though!
Substantially I observed that:
>>> def without_else(param=False):
… if param:
… ….

## Fix Python – A weighted version of random.choice

I needed to write a weighted version of random.choice (each element in the list has a different probability for being selected). This is what I came up with:
def weightedChoice(choices):
“””Like random.choice, but each element can have a different chance of
being selected.

choices can be any iterable containing iterables with two ite….

## Fix Python – Fastest way to list all primes below N

This is the best algorithm I could come up.
def get_primes(n):
numbers = set(range(n, 1, -1))
primes = []
while numbers:
p = numbers.pop()
primes.append(p)
numbers.difference_update(set(range(p*2, n+1, p)))
return primes

>>> timeit.Timer(stmt=’get_primes.get_primes(1000000)’, setup=’import get_primes’).ti….

## Fix Python – Should import statements always be at the top of a module?

PEP 8 states:

Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants.

However if the class/method/function that I am importing is only used in rare cases, surely it is more efficient to do the import when it is needed?
Isn’t this:
class SomeClass(object):

def not….

## Fix Python – Flatten an irregular list of lists

Yes, I know this subject has been covered before (here, here, here, here), but as far as I know, all solutions, except for one, fail on a list like this:
L = [[[1, 2, 3], [4, 5]], 6]

Where the desired output is
[1, 2, 3, 4, 5, 6]

Or perhaps even better, an iterator. The only solution I saw that works for an arbitrary nesting is found in this que….

## Fix Python – How to iterate over a list in chunks

I have a Python script which takes as input a list of integers, which I need to work with four integers at a time. Unfortunately, I don’t have control of the input, or I’d have it passed in as a list of four-element tuples. Currently, I’m iterating over it this way:
for i in range(0, len(ints), 4):
# dummy op for example code
foo += ints….

## Fix Python – How do I profile a Python script?

Project Euler and other coding contests often have a maximum time to run or people boast of how fast their particular solution runs. With Python, sometimes the approaches are somewhat kludgey – i.e., adding timing code to __main__.
What is a good way to profile how long a Python program takes to run?
….