How to solve NameError: name 'xx' is not defined?

I am learning python, according to the logic written in the code in the book, I want to see the running result, the code is as follows, but the output error NameError: name 'pr' is not defined

code show as below:

stack=[]
def pushit():
    stack:append(input(' Enter New String: ').strip())
def popit():
    if len(stack)==0:
        print('Cannot pop from an empty stack!')
    else:
        print ('Removes [','stack.pop()',']')
def viewstack():
    print(stack)
CMDs={'u':pushit,'o':popit,'v':viewstack}
def showmenu():
    pr=''' 
p(U)sh
p(O)p
(V)iew
(Q)uit
Enter choice:'''
while True:
    while True:
        try:
            choice=input(pr).strip()[0].lower()
        except (EOFError,KeyboardInterrupt,IndexError):
            choice='q'
        print('\nYou picked:[%s]'%choice)
        if choice not in 'uovq':
            print('Invalid option,try again')
        else:
            break
        if choice=='q':
            break
        CMDs[choice]()
if _name_=='_main_':
    showmenu()

The error message is as follows：

Traceback (most recent call last):
  File "/Users/oliver/Desktop/test.py", line 22, in <module>
    choice=input(pr).strip()[0].lower()
NameError: name 'pr' is not defined

>Solution :

There are two errors in your code,

1. The logic in the showmenu method needs to be indented
2. _name_=='_main_' -> __name__ == "__main__"

stack=[]
def pushit():
    stack:append(input(' Enter New String: ').strip())
def popit():
    if len(stack)==0:
        print('Cannot pop from an empty stack!')
    else:
        print ('Removes [','stack.pop()',']')
def viewstack():
    print(stack)
CMDs={'u':pushit,'o':popit,'v':viewstack}
def showmenu():
    pr=''' 
    p(U)sh
    p(O)p
    (V)iew
    (Q)uit
    Enter choice:'''
    while True:
        while True:
            try:
                choice=input(pr).strip()[0].lower()
            except (EOFError,KeyboardInterrupt,IndexError):
                choice='q'
            print('\nYou picked:[%s]'%choice)
            if choice not in 'uovq':
                print('Invalid option,try again')
            else:
                break
            if choice=='q':
                break
            CMDs[choice]()

if __name__ == "__main__":
    showmenu()