Python 3 exec 分配错误

Question

我有这个导致我出现问题的 Python 3 代码：

def setStartingVariable(inputType, text, code = None, customErrorMessage = "Error: No error message"):
    while True:
        try:
            variable = inputType(input(text)) # Test if the inputted variable is of the right type. Keep in mind inputType is a variable, not a function.
        except BaseException: 
            print("Error! Try again!")
            continue
        err = 0 # Reset
        if code != None:
            exec(code)
        if err == 0:
            print("No error")
            return variable
        elif err == 1:
            print(customErrorMessage)
        else:
            print("Error: var err != 1 and != 0")


def inputStartingVariables():
    global wallet
    wallet = setStartingVariable(float, "Just type a number in... ", "err = 1", "-!- error message -!-")

inputStartingVariables()

这应该会导致提示...

Just type a number in...

...确实如此。如果我输入浮点数以外的其他内容，则会出现错误...

Error! Try again!

...然后重新提示我。到现在为止还挺好。但是，如果我输入一个正常的数字，它会显示...

No Error

...当它应该显示变量customErrorMessage时，在这种情况下是...

-!- error message -!-

我最初认为问题是在 exec() 函数中，err 没有被视为全局变量，但使用 global err; err = 1 而不仅仅是 err = 1 不会不要修复它。

Answer 1

直截了当：

your err value is never changed .It is always 0

使用exec() 不会改变它

此更改将回答您的问题：

def setStartingVariable(inputType, text, code = None, customErrorMessage = "Error: No error message"):
    while True:
        try:
            variable = inputType(input(text)) # Test if the inputted variable is of the right type. Keep in mind inputType is a variable, not a function.
        except BaseException: 
            print("Error! Try again!")
            continue
        exec_scope = {"err" :0}
         # Reset
        if code != None:
            print ("here")
            exec(code,exec_scope)

        print (code)
        if exec_scope["err"] == 0:
            print("No error")
            return variable
        elif exec_scope["err"] == 1:
            print(customErrorMessage)
        else:
            print("Error: var err != 1 and != 0")


def inputStartingVariables():
    global wallet
    wallet = setStartingVariable(float, "Just type a number in... ", "err = 1", "-!- error message -!-")
inputStartingVariables()

问题原因：

1.exec 是 python3 中的一个函数，所以如果你在其中进行任何变量赋值，它不会改变变量内容，它只能用于 exec 函数

即）

def a():
    exec("s=1")
    print (s)
a()

Traceback (most recent call last):
File "python", line 4, in <module>
File "python", line 3, in a
NameError: name 's' is not defined

有关变量分配的更多信息，您可以通过martin 和blaknight 看到这两个问题

编辑：

def setStartingVariable(inputType, text, code = None, customErrorMessage = "Error: No error message"):
    global err
    while True:
        try:
            variable = inputType(input(text)) # Test if the inputted variable is of the right type. Keep in mind inputType is a variable, not a function.
        except BaseException: 
            print("Error! Try again!")
            continue

        err = 0 # Reset
        if code != None:
            exec("global err;"+code)
            print (err)
        if err == 0:
            print("No error")
            return variable
        elif err == 1:
            print(customErrorMessage)
        else:
            print("Error: var err != 1 and != 0")


def inputStartingVariables():
    global wallet
    wallet = setStartingVariable(float, "Just type a number in... ", "err = 1", "-!- error message -!-")

inputStartingVariables()