如何从python中的字符串中检测正确的变量？

def check_variable(string):
    try:
        eval(string)
        return True
    except NameError:
        return False

string = "x = 5"
print(check_variable(string))  # 输出：True

string = "y = z + 2"
print(check_variable(string))  # 输出：False

def check_variable(string):
    variables = string.split("=")[0].strip().split(",")
    for variable in variables:
        if variable.strip() not in locals():
            return False
    return True

string = "x = 5"
print(check_variable(string))  # 输出：True

string = "y = z + 2"
print(check_variable(string))  # 输出：False