正则表达式如何检查子字符串列表是否出现在字符串之前？

Question

I have tried to searched it but no specific answer.

I would like to identify the string I want to use depending on the characters appears before it.

What I like to do is, For example:

def check_if_char_appears(input_string):
    substring_list = ['aa', 'bb', 'dd', 'ef']
    for i in substring_list:
        if i appears right before 'cake':
           return True
    return False

result: Condition1:

input_string = 'aacake'
check_if_char_appears(input_string)

is True

Condition2:

input_string = 'aakkcake'
check_if_char_appears(input_string)

is False

found the java solution could do the funcion "if i appears before 'cake':"

str.matches("i*(?<!\\.)cake.*");

but I dont know how to do with python the this function.. could some one kindly help me with this (or tell me how to look this up in google?)

Thanks!

Answer 1

for simple case like yours.

substring_list = ['aa', 'bb', 'dd', 'ef']
for i in substring_list:
    if "{}cake".format(i) in input_string:
        return True

Answer 2

Using regex

matches = re.match(r'.*(aa|bb|dd|ef)cake.*', your_str)
if matches:
    # do whatever you want

If you want nothing after the cake

matches = re.match(r'.*(aa|bb|dd|ef)cake', your_str)
if matches:
    # do whatever you want

Answer 3

You can use regex here. you can make regex on the go like.

substring_list = ['aa', 'bb', 'dd', 'ef']
if re.match(r"({})cake".format("|".join(substring_list)), input_string):
    return True

long answer:

def check_if_char_appears(input_string):
    substring_list = ['aa', 'bb', 'dd', 'ef']
    sub_string_re = "|".join(substring_list) # 'aa|bb|dd|ef'
    re_string = r"({})cake".format(sub_string_re) # (aa|bb|dd|ef)cake
    if re.match(re_string, input_string):
        return True
    return False


input_string = 'aacake'
print(check_if_char_appears(input_string))

input_string = 'aakkcake'
print(check_if_char_appears(input_string))

out:

True
False

Answer 4

There is a regex module in python ( https://docs.python.org/3.6/library/re.html )

That should do exactly the same thing just with

import re
m = re.search("i*(?<!\\.)cake.*", your_string)
for match in m:
  print(m)