Python 黑魔法（持续收录）
zip 对矩阵进行转置
a = [[1, 2, 3], [4, 5, 6]]print(list(map(list, zip(*a))))
zip 反转字典
a = dict(a=1, b=2, c=3)print(dict(zip(a.values(), a.keys())))
将list分成n份
print(list(zip(*(iter([1, 2, 3, 4, 5, 6]),) * 3)))# [(1, 2, 3), (4, 5, 6)]
all & any 函数
- all:如果iterable的所有元素不为0、''、False或者iterable为空，all(iterable)返回True，否则返回False
- any: 如果所有元素中有一个值不是0、''或False，那么结果就为True，否则为False
print(any([]))# Falseprint(all([]))# Trueprint(all([1,2,3,0]))# False
Concatenate long strings elegantly across line breaks in code
my_long_text = ("We are no longer the knights who say Ni! " "We are now the knights who say ekki-ekki-" "ekki-p'tang-zoom-boing-z'nourrwringmm!")print(my_long_text)# We are no longer the knights who say Ni! We are now the knights who say ekki-ekki-ekki-p'tang-zoom-boing-z'nourrwringmm! calling different functions with same arguments based on condition
def product(a, b): return a * bdef subtract(a, b): return a - bb = Trueprint((product if b else subtract)(1, 1))
Sort dict keys by value
d = {'apple': 10, 'orange': 20, 'banana': 5, 'rotten tomato': 1}print(sorted(d, key=d.get))# ['rotten tomato', 'banana', 'apple', 'orange'] exec
exec("print('Hello ' + s)", {'s': 'World!'})# exec can be used to execute Python code during runtime variables can be handed over as a dict unpacking
[(c, *d, [*e]), f, *g] = [[1, 2, 3, 4, [5, 5, 5]], 6, 7, 8]print(c, d, e, f, g)# 1 [2, 3, 4] [5, 5, 5] 6 [7, 8]
flatten list
import itertoolsa = [[1, 2], [3, 4], [[5,6],[7,8]]]print(list(itertools.chain(*a)))# [1, 2, 3, 4, [5, 6], [7, 8]]
把嵌套的也flatten？
a = [[1, 2], [3, 4], [[5, 6], [7, 8]]]a = eval('[%s]' % repr(a).replace('[', '').replace(']', ''))print(a)# [1, 2, 3, 4, 5, 6, 7, 8] 更简单？
a = [[1, 'a', ['cat'], 2], [[[3], 'a', 'm', [1, 2, 3], [1, [1, 2, 3]]]], 'dog']flatten = lambda L: eval(str(L).replace('[', '*[')[1:])flatten(a) dict求交
dctA = {'a': 1, 'b': 2, 'c': 3}dctB = {'b': 4, 'c': 3, 'd': 6}# loop over dicts that share (some) keys in Python3for ky in dctA.keys() & dctB.keys(): print(ky)# loop over dicts that share (some) keys and values in Python3for item in dctA.items() & dctB.items(): print(item) split a string max times
"""split a string max times"""string = "a_b_c"print(string.split("_", 1))# ['a', 'b_c']"""use maxsplit with arbitrary whitespace"""s = "foo bar foobar foo"print(s.split(None, 2))# ['foo', 'bar', 'foobar foo'] 字典合并
d1 = {'a': 1}d2 = {'b': 2}# python 3.5print({**d1, **d2})print(dict(d1.items() | d2.items()))d1.update(d2)print(d1) Find Index of Min/Max Element
lst = [40, 10, 20, 30]def minIndex(lst): return min(range(len(lst)), key=lst.__getitem__) # use xrange if < 2.7def maxIndex(lst): return max(range(len(lst)), key=lst.__getitem__) # use xrange if < 2.7print(minIndex(lst))print(maxIndex(lst))
remove duplicate items from list and keep order
from collections import OrderedDictitems = ["foo", "bar", "bar", "foo"]print(list(OrderedDict.fromkeys(items).keys()))
set global variables from dict
def foo(): d = {'a': 1, 'b': 'var2', 'c': [1, 2, 3]} globals().update(d)foo()print(a, b, c) Sort a list and store previous indices of values
l = [4, 2, 3, 5, 1]print("original list: ", l)values, indices = zip(*sorted((a, b) for (b, a) in enumerate(l)))# now values contains the sorted list and indices contains# the indices of the corresponding value in the original listprint("sorted list: ", values)print("original indices: ", indices)# note that this returns tuples, but if necessary they can# be converted to lists using list() None
from collections import defaultdicttree = lambda: defaultdict(tree)users = tree()users['harold']['username'] = 'chopper'users['matt']['password'] = 'hunter2'
for_else 跳出多层循环
for i in range(5): for j in range(6): print(i * j) if i * j == 20: break else: continue break