I am trying to create a loop that matches user entered input to a key from defined dictionary and returns the corresponding value as an output. However, when the user inputs something that is not in keys, the program prints None and it terminates. But I want the program to continue to let the user enter an input until it finds a match on one of the keys, and it should terminate only when user has provided an input key that is in present the dictionary. I am new to Python so am not sure how to use while statement to loop the process. Appreciate any help.

list_dict = {"James" : "Pen Set", "Tim" : "Geometry Box", "Rocky" : "Sticky Notes" , "Jeff" : "Alarm Clock" , "Sandy" : "Highlighters"}
_name = input("Enter Name: ")
x = list_dict.get(_name)
while x == None:
  _name = input("Re-Enter Name: ")
  x = list_dict.get(_name)
  break
else:
  print(_name, "got", x)
break

CodePudding user response：

You are using the break keyword directly inside a while-loop without any condition. The result is that the loop content can only run once before exiting the loop. If you wish to keep the loop running, remove the break keyword.

Here is a sample answer to your question:

list_dict = {"James" : "Pen Set", "Tim" : "Geometry Box", "Rocky" : "Sticky Notes" , "Jeff" : "Alarm Clock" , "Sandy" : "Highlighters"}

# first input
_name = input("Enter Name: ")
# obtain x
x = list_dict.get(_name)

# perform checking on the latest value of x
while x == None:
  _name = input("Re-Enter Name: ")
  x = list_dict.get(_name)
  # if x is a valid value, the while statement above will detect this and terminate the loop

# final output
print(_name, "got", x)

Remark 1: keep in mind that loops can be terminated automatically by setting the loop condition correctly. Arbitrary use of break and continue keywords is generally advised against due to its disruption to normal programme flow.

Remark 2: using else keyword with while keyword on the same level means that the else block is only executed if the while-loop completes its execution without any interruptions, i.e. never encountering the break keyword. This is inapplicable to your case, since the termination condition is simple, and there is no need to detect if the while-loop is interrupted.

CodePudding user response：

The problem is the break statement. If you remove it, the program should work fine ;)

CodePudding user response：

The provided code only requires a minor change to produce the behavior that you expect. In the following modified code, both break statements have been removed:

list_dict = {"James" : "Pen Set", "Tim" : "Geometry Box", "Rocky" : "Sticky Notes" , "Jeff" : "Alarm Clock" , "Sandy" : "Highlighters"}
_name = input("Enter Name: ")
x = list_dict.get(_name)
while x == None:
  _name = input("Re-Enter Name: ")
  x = list_dict.get(_name)
  # break
else:
  print(_name, "got", x)
# break

Explanation

• Remove the first break to prevent the while loop from always exiting after the first iteration. If the user-provided name does not exist in list_dict, we want the while loop to continue iterating. By placing a break, we are forcing the while loop to exit after the first iteration. It's also important to note that a break causes an else clause to be skipped. With the original code, if the first name entered does not exist, but the second name entered does exist, the break causes the else clause to be skipped and the print statement is not executed.
• Remove the second break because it is only applicable when placed inside a loop.

Refer to the documentation for the break statement for additional information.

Testing the modified code

Enter Name: TestName1
Re-Enter Name: TestName2
Re-Enter Name: Jeff
Jeff got Alarm Clock

CodePudding user response：

I improved a little of your code and i think this help to solve your problem.

list_dict = {"James" : "Pen Set", "Tim" : "Geometry Box", "Rocky" : 
"Sticky Notes" , "Jeff" : "Alarm Clock" , "Sandy" : "Highlighters"}
_name = input("Enter Name: ")

while _name not in list_dict.keys():
   _name = input("Re-Enter Name: ")
print(f'{_name} got {list_dict.get(_name)}')