python - 使用多个（相似的）生成器表达式

Question

在 csv 文件中，我试图用其他字符替换某些字符。

我当前的代码与此类似：

import csv

set1 = set('abc')
set2 = set('def')
set3 = set('ghi')

with open(path, 'r') as input, open(path2, 'w') as output:
    reader = csv.reader(input)
    writer = csv.writer(output)

    for row in reader:
            newrow = row
            newrow = [''.join('x' if c in set1 else c for c in item) for item in newrow]
            newrow = [''.join('y' if c in set2 else c for c in item) for item in newrow]
            newrow = [''.join('z' if c in set3 else c for c in item) for item in newrow]

            writer.writerow(newrow)

在这个例子中，我只使用了三个生成器表达式，但很容易不止这些。

有谁知道这样做的正确方法？我担心这种结构可能不是最快的（当然看起来也不是最优的）。

Answer 1

您可以使用循环并参数化不同的部分：

newrow = row
for v, s in (('x', set1), ('y', set2), ('z', set3)):
    newrow = [''.join(v if c in s else c for c in item) for item in newrow]

如果要替换字符，请不要使用集合，而是使用映射：

mapping = dict.fromkeys(set1, 'x')
mapping.update(dict.fromkeys(set2, 'y'))
mapping.update(dict.fromkeys(set3, 'z'))
for row in reader:
    newrow = [''.join(mapping.get(c, c) for c in item) for item in newrow]

Answer 2

str.translate可能是合适的；类似的东西

replacements = [
    ('abc', 'x'),
    ('def', 'y'),
    ('ghi', 'z'),
]

trans = str.maketrans({ k: v for l, v in replacements for k in l })

和

new_row = [item.translate(trans) for item in row]

Answer 3

Here is something that combines both answers in some way and works great (multiple times faster than the code in the question):

replacements = [
('abc', 'x'),
('def', 'y'),
('ghi', 'z'),
]

mapping = {a: b for c, b in replacements for a in c}

for row in reader:
    newrow = [''.join(mapping.get(c, c) for c in item) for item in row]
    writer.writerow(newrow)