拆分包含python中数学运算符的字符串

Question

世界！，我今天早些时候遇到了一个问题。除数字和变量外，我还试图拆分操作。它会将+、-、/、*与数字或变量分开(例如: 10+11+10在代码中，而*中则有一个列表)

我的代码：

x = "100+20+a"

operators = ["*","/","+","-"]

def get_index_of(OP,txt):
  return [v for v,i in enumerate(txt+"+") if i == OP]

l = []
for i in operators:
  l.append(get_index_of(i,x))

spliting = sum(l,[])

out = []
for j in spliting:
  out.append(x)
  x = x[:j]

print(out)

我得到的输出：

['100+20+a', '100', '100']

我想要的输出：

["100","+","20","+","a"]

Answer 1

使用堆栈

def parse(expression, operators = ["*","/","+","-"]):
    stack = ['']               # start with empty string on stack
    for c in expression:
        if c in operators:
            stack.append(c)    # place operator as new element on stack
            stack.append('')
        elif c != " ":         # not a space
            stack[-1] += c     # append to last element on stack
            
    return stack

示例

print(parse("100+20+a"))
# Output: ['100', '+', '20', '+', 'a']

Answer 2

尝试：

from itertools import groupby

x = "100+20+a"
operators = {"*", "/", "+", "-"}  # <-- use set instead of a list

out = ["".join(g) for _, g in groupby(x, operators.__contains__)]
print(out)

指纹：

['100', '+', '20', '+', 'a']

Answer 3

如果您对第三方工具开放--有一个简单的方法：

它很容易转换到您想要的功能。

from more_itertools import split_at

>>>lst = list(split_at(x, lambda x: x == '+', keep_separator=True))
                       
>>>lst
                       
[['1', '0', '0'], ['+'], ['2', '0'], ['+'], ['a']]
outs = [''.join(x) for x in lst]
                       
>>>outs
                       
['100', '+', '20', '+', 'a']

# or doing in one shot:
>>>final = [''.join(x) for x in split_at(x, lambda x: x == '+', keep_separator=True)]