not a python dev, but:

- python probably has a lib like underscore (reduce map filter etc), could help

- check out the quake source code, any version, its huge and the entire thing is not only readable but possibley a work of art.

- have you tried lambdas? to some its more readable.. ex:

    nums = range(2,50)
    for i in range(2, 8):
        nums = filter(lambda x: x == i or x % i, nums)

personally when i have too complex process i like to go more functional, ex:

    main:
        prepare_data1()
        prepare_data2()
        do_long_stuff()
        nextstep()

that allows me to focus on only on building one step and still have readable code.

many game-devs prefer breaking their project into many tiny files with a specific purpose instead of spaghetti, ex:

    file.py
    parser.py
    display.py
    function1.py
    function2.py

its also a bit easier to nav around the project and make sense of it this way. you might want to check out rust or D or F or another lang also.