Python通过30秒就能学会的漂亮短程序代码(过程全解)

def initialize_2d_list(w, h, val=None):
    return [[val for x in range(w)] for y in range(h)]

>>> initialize_2d_list(2,2)
[[None, None], [None, None]]

>>> initialize_2d_list(2,2,0)
[[0, 0], [0, 0]]

def bifurcate_by(lst, fn):
    return [
      [x for x in lst if fn(x)],
      [x for x in lst if not fn(x)]
    ]

>>> bifurcate_by(['beep', 'boop', 'foo', 'bar'], lambda x: x[0] == 'b') 
[['beep', 'boop', 'bar'], ['foo']]

def intersection_by(a, b, fn):
    _b = set(map(fn, b))
    return [item for item in a if fn(item) in _b]

>>> from math import floor
>>> intersection_by([2.1, 1.2], [2.3, 3.4],floor)
[2.1]

def max_element_index(arr):
    return arr.index(max(arr))

>>> max_element_index([5, 8, 9, 7, 10, 3, 0])
4

def symmetric_difference(a, b):
    _a, _b = set(a), set(b)
    return [item for item in a if item not in _b] + [item for item in b if item not in _a]

>>> symmetric_difference([1, 2, 3], [1, 2, 4])
[3, 4]

def clamp_number(num,a,b):
    return max(min(num, max(a,b)),min(a,b))

>> clamp_number(2,3,10)
3

>> clamp_number(7,3,10)
7

>> clamp_number(124,3,10)
10

def map_values(obj, fn):
    ret = {}
    for key in obj.keys():
        ret[key] = fn(obj[key])
    return ret

>>> users = {
...   'fred': { 'user': 'fred', 'age': 40 },
...   'pebbles': { 'user': 'pebbles', 'age': 1 }
... }

>>> map_values(users, lambda u : u['age'])
{'fred': 40, 'pebbles': 1}

>>> map_values(users, lambda u : u['age']+1)
{'fred': 41, 'pebbles': 2}

def decapitalize(s, upper_rest=False):
    return s[:1].lower() + (s[1:].upper() if upper_rest else s[1:])

>>> decapitalize('FooBar')
'fooBar'

>>> decapitalize('FooBar', True)
'fOOBAR'

def sum_by(lst, fn):
    return sum(map(fn,lst))

>>> sum_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }], lambda v : v['n'])
14

def count_occurrences(lst, val):
    return len([x for x in lst if x == val and type(x) == type(val)])

>>> count_occurrences([1, 1, 2, 1, 2, 3], 1)
3

from math import ceil
def chunk(lst, size):
	return list (
		map(lambda x:lst[x * size:x * size + size],
			list(range(0, int(ceil(len(lst) / size))))))

chunk([1,2,3,4,5],2)
# [[1,2],[3,4],5]

def digitize(n):
    return list(map(int, str(n)))

digitize(123)
# [1, 2, 3]

def fibonacci(n):
	if n <= 0:
		return [0]
	sequence = [0, 1]
	while len(sequence) <= n:
		next_value = (sequence[len(sequence) - 1] + sequence[len(sequence) - 2])
		sequence.append(next_value)
	return sequence

fibonacci(7)
# [0, 1, 1, 2, 3, 5, 8, 13]

from re import sub

def snake(s):
	return '_'.join(
		sub('([A-Z][a-z]+)', r' 1',
		sub('( [A-Z]+)', r' l1',
		s.replace('-', ' '))).split()).lower()

snake('camelCase')# 'camel_case'

snake('some text')# 'some_text'

snake('some-mixed_string With spaces_underscores-and-hyphens')# 'some_mixed_string_with_spaces_underscores_and_hyphens'

snake('AllThe-small Things')# "all_the_small_things"