Nice solution, it's compact and simple to understand. There is little to improve, few suggestions:

• Imports: there are a lot of imports, maybe leftovers of previous attempts.
• Try Except block: should be around the code that can cause the exception.

Applying the suggestions:

import re

class Solution:
    def myAtoi(self, s: str) -> int:
        MAX, MIN = 2147483647, -2147483648
        s = re.findall(r'^\s*[+-]?\d+', s)
        try:
            res = int(''.join(s))
        except:
            return 0
        if res > MAX:
            return MAX
        if res < MIN:
            return MIN
        return res

Performance

Runtime: 36 ms, faster than 51.56% of Python3 online submissions
Memory Usage: 14.1 MB, less than 32.27% of Python3 online submissions

Regex makes the code compact but is not the fastest approach. Faster solutions iterate through the string character by character.

If you're so keen on getting exactly the functionality of c's atoi, why not use it directly? E.g., on my Mac,

>>> import ctypes, ctypes.util
>>> whereislib = ctypes.util.find_library('c')
>>> whereislib
'/usr/lib/libc.dylib'
>>> clib = ctypes.cdll.LoadLibrary(whereislib)
>>> clib.atoi('-99foobar')
-99

In Linux, Windows, etc, identical code should work except that you'll see a different path if you examine whereislib (only on really, really peculiar installations should this code ever fail to find the C runtime library).

If you're keen on avoiding direct C library usage, I guess you could grab the relevant prefix, e.g. with a RE such as r'\s*([+-]?\d+)', and try int on that.

Refer to a basic atoi in C:

int myAtoi(char *str)
{
    int res = 0; // Initialize result

    // Iterate through all characters of input string and update result
    for (int i = 0; str[i] != '\0'; ++i)
        res = res*10 + str[i] - '0';

    // return result.
    return res;
}

Which translates into the Python:

def atoi(s):
    rtr=0
    for c in s:
        rtr=rtr*10 + ord(c) - ord('0')

    return rtr

Test it:

>>> atoi('123456789')
123456789   

If you want to accommodate an optional sign and whitespace the way that int does:

def atoi(s):
    rtr, sign=0, 1
    s=s.strip()
    if s[0] in '+-':
        sc, s=s[0], s[1:]
        if sc=='-':
            sign=-1

    for c in s:
        rtr=rtr*10 + ord(c) - ord('0')

    return sign*rtr

Now add exceptions and you are there!