How do i access a class through input

Question

I put together a small test code just to demonstrate the error I am getting when trying to enter a class with input. Nothing pretty or good its just to get the specific error across.

Code:

class people(object):
    def deposit():
        print("depositing")
    def withdraw():
        print("withdrawing")
John = people()
selection = input("Type John: ")
selection.deposit

Error:

[evaluate classes.py]
Type John: John
Traceback (most recent call last):
  File "c:\Users\Peter\Desktop\Desktop 2\Python\classes.py", line 9, in module
    selection.deposit
builtins.AttributeError: 'str' object has no attribute 'deposit'

Answer 1

If it's only for demonstration purposes you could lookup the selection value in the locals() dict:

In [4]: John = 1

In [5]: selection = "John"

In [6]: locals()[selection]
Out[6]: 1

So, your code would look like:

class people(object):
    def deposit(self):
        print("depositing")
    def withdraw(self):
        print("withdrawing")
John = people()
selection = input("Type John: ")
locals()[selection].deposit()

However, please do not use this approach in production code. There are better patterns for dispatching stuff to objects..

Answer 2

Generally, you don't want this kind of direct correspondence between user input and your internal variable names. You'd have some data structure to keep track of your people instances, perhaps a dict:

known_people = {'John': people(), 'Jake': people(), 'Jeffrey', people()}

and you'd process user input to determine what to do with your data:

selected_person = known_people[selection]
selected_person.deposit()

While you technically can access variables dynamically:

John = people()
selected_person = locals()[selection]

you really, really shouldn't. It doesn't scale well to more complex data, and it introduces potential for lots of nasty bugs.

Answer 3

<<<<<< 答案在这里 << >> 和这里 >>>>>>

Answer 4

You could store the people (like John) in a separate object (like a dictionary).

Consider that approach:

class Man(object):
    # I renamed the `people` class to `Man` since it's representing a single man (like John).
    # You also have to add a required `self` parameter for every function inside of the class!
    def deposit(self):
        print("depositing")

    def withdraw(self):
        print("withdrawing")

# We'll make `people` a dictionary instead.
people = {
    'John': Man()
}

selection = raw_input("Type John: ")

# You have to put parentheses there so the `deposit()` function would call
people[selection].deposit()

eval() is pretty evil , so as locals() .

Answer 5

input("Type John: ") returns a string, not an object of type people so you can't call the method deposit on it.

Workaround-

class people(object):
    def deposit(self):
        print("depositing")
    def withdraw(self):
        print("withdrawing")
selection = input("Type people(): ")
selection.deposit()

Input-

people()  

Output-

depositing