## 列表数据的过滤、修改、和替换
1 # 使用推导式过滤、修改和替换数据 2 nums = [10,4,33,-54,54,-6,34,-5,23,56,-87,43,-4,3] 3 new_nums = [i for i in nums if i >= 0] # 过滤掉小于0的元素 4 print(new_nums) 5 # [10, 4, 33, 54, 34, 23, 56, 43, 3] 6 7 new_nums = [abs(i) for i in nums] # 将所有元素值修改为其绝对值 8 print(new_nums) 9 # [10, 4, 33, 54, 54, 6, 34, 5, 23, 56, 87, 43, 4, 3] 10 11 new_nums = [i if i >= 0 else 0 for i in nums] # 将小于0的元素替换为0 12 print(new_nums) 13 # [10, 4, 33, 0, 54, 0, 34, 0, 23, 56, 0, 43, 0, 3] 14 15 # 使用生成器表达式操作列表以节省内存 16 new_nums = (i for i in nums if i >= 0) 17 print(new_nums) 18 # <generator object <genexpr> at 0x7f4bebb01048> 19 20 # 对于过滤条件比较复杂的列表，使用filter()函数进行过滤 21 22 def is_int(item): 23 try: 24 int(item) 25 return True 26 except ValueError: 27 return False 28 29 items = ['a', '1', '-28', '2.42', 'b', '-8.34'] 30 print(list(filter(is_int, items))) 31 # ['1', '-28'] 32 33 # itertools.compress()过滤数据 34 from itertools import compress 35 36 37 nums = [10,4,33,-54,54,-6,34,-5,23,56,-87,43,-4,3] 38 is_greater_than_0 = [i > 0 for i in nums] # 创建布尔值序列 39 print(is_greater_than_0) 40 # [True, True, True, False, True, False, True, False, True, True, False, True, False, True] 41 42 print(list(compress(nums, is_greater_than_0))) # 为True的被保留，为False的被过滤 43 # [10, 4, 33, 54, 34, 23, 56, 43, 3]
参考资料：
Python Cookbook, 3rd edition, by David Beazley and Brian K. Jones (O’Reilly).