BOJ - 3613 - Java vs C++

def solution():
    variables = str(input())

    if variables.find('_') >= 0:
        if variables[0] == '_':
            print("Error!")
            return

        for i in range(len(variables)):
            if "A" <= variables[i] and variables[i] <= "Z" :
                print("Error!")
                return

        cVariable = variables.split('_')
        for i in range(1, len(cVariable)):
            if not cVariable[i]:
                print("Error!")
                return

            cVariable[i] = cVariable[i][0].upper() + cVariable[i][1:]
        print(''.join(cVariable))
    else:
        if "A" <= variables[0] and variables[0] <= "Z":
            print("Error!")
            return
        javaVariable = []
        start = 0
        for i in range(0, len(variables)):
            if "A" <= variables[i] and variables[i] <= "Z" :
                javaVariable.append(variables[start:i].lower())
                start = i
        javaVariable.append(variables[start:].lower())
        print('_'.join(javaVariable))

solution()

https://www.acmicpc.net/problem/3613