Question

我尝试编写程序但遇到了return语句的问题。

以下代码行引发了一条错误消息，指出变量names未定义。

但是，我确实使用return语句返回names并将其传递给main函数：

def main(names):
    names_in()
    print(names)

# import the record, put it into a list,  pass that list to main().
def names_in():
    infile = open('names.txt','r')
    names = infile.readlines()

    infile.close()

    index = 0
    while index < len(names):
        names[index] = names[index].rstrip('\n')
        index += 1
    return names

main(names)

我之前写过另一个程序也做了同样的事情，一切正常，所以我不确定这里有什么问题？

Answer 1

你的问题在这里：

main(names)

您正在使用尚未定义的变量名称调用main函数。您得到的错误应显示指向此行的行号：这将验证问题所在。

# 'names' is not defined in this scope
def main(names):
    # Some code
    # 'names' is a variable that is 'in scope' here because it's passed as an 'argument'

# 'names' is not defined in this scope either

# import the record, put it into a list,  pass that list to main().
def names_in():
    infile = open('names.txt','r')
    names = infile.readlines()  # defines 'names' for this scope

    # more code
    return names  # because 'names' is defined it can return it

# 'names' is no longer defined in this scope
main(names)  # This fails because when the compiler tries to resolve 'names' it can't find anything

根据您显然要做的事情，您需要修改main功能，如下所示：

def main():
    print(names_in())

并称之为：

main()

请注意，您似乎对如何执行代码感到困惑。如果我写：

def a():
    print("a")

def b():
    print("b")

print("c")
b()
a()

它被翻译成等同于：

的东西

print("c")
print("b")
print("a")

将def语句有效地复制粘贴到调用它们的位置。

Answer 2

您的main函数不应包含任何参数。相反，它应该使用names_in的返回值：

def main():
    names = names_in()
    print(names)

稍后在您的代码中：

main()

python中的return语句

2 个答案: