Builtin functions

https://docs.python.org/3/library/functions.html

INTRODUCTION

Builtin functions are always available.

# Builtin objects in Python 2.

import __builtin__   # Py2
dir(__builtin__)   # list of objects

# Builtin objects in Python 3.

import builtins   # Py3
dir(builtins)   # list of objects
zip is builtins.zip   # True
zip = my_better_zip

Type names: basestring(), bool(), bytearray(), bytes(), complex(), dict(), float(), frozenset(), int(), list(), long() [Py2], set(), str(), tuple(), unicode() [Py2].

Mathematical functions and tools: abs(), all(), any(), ascii() [Py3], bin() , chr(), divmod(), enumerate(), eval(), exec(), filter() format(), hex(), iter(), len(), map(), max(), min(), next() [Py2.6+], oct(), open(), ord(), pow(), range(), repr(), reversed(), round(), sorted(), sum(), unichr() [Py2], xrange() [Py2], zip().

OOP: classmethod(), delattr(), dir(), getattr(), hasattr(), isinstance(), issubclass(), object(), property(), setattr(), staticmethod(), super(), type().

FUNCTIONS FOR ITERABLES

# zip(*iterables) return a zip object
# zip(*iterables, strict=False) in Py3.10
# The strict=True is used to test if the lengths of iterables are identical.
# Iterate over several iterables in parallel, producing tuples with an item from each one.
# By default, zip() stops when the shortest iterable is exhausted.

list(zip([1, 2, 3], 'abc'))   # [(1, 'a'), (2, 'b'), (3, 'c')]

list(zip([1, 2], 'abcd'))   # [(1, 'a'), (2, 'b')], different lengths

# map(function, iterable, ...) return a map object (iterator) in Py3

def cube(x):
    return x * x * x

list(map(cube, range(10)))   # map object
list(cube(x) for x in range(10))   # generator object
# [0, 1, 8, 27, 64, 125, 216, 343, 512, 729]

L = [(1, 2), (3, 4, 5)]
list(map(sum, L))   # [3, 12] map object
list(sum(t) for t in L)   # [3, 12] generator object

L = [1, 2, 3]
M = [4, 5, 6]
list(map(sum, zip(L, M)))   # [5, 7, 9]
list(sum(t) for t in zip(L, M))

def calc(x, y):   # two arguments and two iterables in map()
    return 2 * x + y

R = range(10)
list(map(calc, R, R))
list(calc(x, y) for (x, y) in zip(R, R))
# [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

# filter(function or None, iterable) return a filter object (iterator) in Py3

def check(x):
    return x % 2 != 0 and x % 3 != 0

list(filter(check, range(30)))   # filter object
list(x for x in range(30) if check(x))   # generator object, equivalent
# [1, 5, 7, 11, 13, 17, 19, 23, 25, 29]

list(filter(None, [-2,-1,0,1,2]))   # [-2, -1, 1, 2] filter object
list(x for x in [-2,-1,0,1,2] if x)   # generator object, equivalent

# Testing speed.

import random
import timeit

L = [random.random() for x in range(1000000)]

func = (lambda x: x < 0.5)

t1 = timeit.Timer(lambda: sum(x for x in L if x < 0.5))
print(t1.timeit(1))   # 0.028795670999897993 best

t2 = timeit.Timer(lambda: sum(x for x in L if func(x)))
print(t2.timeit(1))   # 0.06057641600000352

t3 = timeit.Timer(lambda: sum(filter((lambda x: x < 0.5), L)))
print(t3.timeit(1))   # 0.049515714000108346

t4 = timeit.Timer(lambda: sum(filter(func, L)))
print(t4.timeit(1))   # 0.0439489059999687