python - 正则表达式避免不必要的组

Question

我有这个代码:

string = """a = 10 + 15
b = 50 + b
c = a + b
d = c + 50"""


letter = "([a-z])"
signs = "(\+|\-|\*|\/)"
regex = re.compile(r"{0} = (\d+) {1} (\d+)|"
                   r"{0} = (\d+) {1} {0}|"
                   r"{0} = {0} {1} {0}|"
                   r"{0} = {0} {1} (\d+)".format(letter, signs))signs))(\d+)".format(letter,signs))

如果我执行 re.search(regex,string).groups() 我最终会得到

('a', '10', '+', '15', None, None, None, None, None, None, None, None, None, None, None, None)
(None, None, None, None, 'b', '50', '+', 'b', None, None, None, None, None, None, None, None)
(None, None, None, None, None, None, None, None, 'c', 'a', '+', 'b', None, None, None, None)
(None, None, None, None, None, None, None, None, None, None, None, None, 'd', 'c', '+', '50')

但我只想要 4 个组。 [变量，val1，运算符，val2]

我正在使用列表理解

[r for r in re.search(regex,string).groups() if r != None]

但我想知道是否有办法在正则表达式本身中做到这一点。

Answer 1

在这种情况下，最好将正则表达式从四个单独的语句简化为一个稍微重载的语句，这确实需要修改字母:

letter = "[a-z]"
signs = "(\+|\-|\*|\/)"
regex = re.compile(r"({0}) = (\d+|{0}) {1} (\d+|{0})".format(letter, signs))signs))(\d+)".format(letter,signs))