如何区分字符串中的“0”和“00”以及如何替换子字符串

def distinguish_zero_and_double_zero(s, start_index):
    substring = s[start_index:start_index+1]
    if len(substring) == 1:
        return "0"
    elif len(substring) == 2:
        return "00"
    else:
        return "Unknown"

# 示例
s = "12300450"
print(distinguish_zero_and_double_zero(s, 3))  # 输出: 00
print(distinguish_zero_and_double_zero(s, 6))  # 输出: 0

import re

def distinguish_zero_and_double_zero(s, start_index):
    match = re.match(r'0{1,2}', s[start_index:])
    if match:
        return match.group()
    else:
        return "Unknown"

# 示例
s = "12300450"
print(distinguish_zero_and_double_zero(s, 3))  # 输出: 00
print(distinguish_zero_and_double_zero(s, 6))  # 输出: 0

def replace_substring(s, old, new):
    return s.replace(old, new)

# 示例
s = "12300450"
new_s = replace_substring(s, "00", "0")
print(new_s)  # 输出: 1230450

import re

def replace_substring_with_regex(s, pattern, new):
    return re.sub(pattern, new, s)

# 示例
s = "12300450"
new_s = replace_substring_with_regex(s, r'0{2}', '0')
print(new_s)  # 输出: 1230450