Python 代码阅读（第 6 篇）：根据给定的函数对列表中的元素进行分组

def group_by(lst, fn):  return {key : [el for el in lst if fn(el) == key] for key in map(fn, lst)}
# EXAMPLESfrom math import floorgroup_by([6.1, 4.2, 6.3], floor) # {4: [4.2], 6: [6.1, 6.3]}group_by(['one', 'two', 'three'], len) # {3: ['one', 'two'], 5: ['three']}

{ key_expr: [x for x in collection2 if condition2] for value in collection1 if condition1 }

>>> d = {'one': 1, 'two': 2, 'three': 3, 'two': 2}>>> d{'one': 1, 'two': 2, 'three': 3}>>> d = {'one': 1, 'two': 2, 'three': 3, 'two': 22}>>> d{'one': 1, 'two': 22, 'three': 3}>>>