CODEWITHSUNDEEP
pythonloopsdictionaryiteration
Khalil
Khalil

Reputation: 51

Why python print the last key

I am new in python and wondering about the result. I just want to understand it. suppose I have the following dictionary:

employee = {   
   'user_name': 'my name',   
   'password': 'hello',   
   'mobile phone': 123456789
}

for i in employee:    
    print(i)  

print(i)

and here is the result:

user_name
password
​mobile phone​
mobile phone

if you notice that the (mobile phone) has been printed twice.the second one comes from the second print in the above code.

  1. Why this is happen? I expected to get this error:

NameError: name 'i' is not defined

as usual by python.

  1. what if I want to access the first or second key? can I access with the same what I access the last one (without writing the key name or number)?

Upvotes: 1

Views: 63

Answers (2)

jossefaz
jossefaz

Reputation: 3932

Your problem here is the scope :

Python's scope behavior is defined by function scope : please see here for more documentation

Since you are running into the main function, the i var will still be defined in the print statement , because it is in the same scope of the for loop.

So it will have the value of the last iteration of your loop (i.e "mobile phone")

#global scope (main function)
 employee = {   
   'user_name': 'my name',   
   'password': 'hello',   
   'mobile phone': 123456789
}

for i in employee:   
    #you are still in the global scope here !!
    print(i)  

#and here too....so the "i" variable will have the value of your last iteration !
print(i)

To be more clear, if you would write something like :


    #global scope (main function)
     employee = {   
       'user_name': 'my name',   
       'password': 'hello',   
       'mobile phone': 123456789
    }
    def show_employees() :
        for i in employee:   
            #you are in the "show_employees" function scope here !!
            print(i)  

    show_employees() # here you call the function

    #and here you will get your "expected error" because "i" is not defined in the global scope
    print(i)

Output :

File "main.py", line 18, in print(i) NameError: name 'i' is not defined

Upvotes: 2

Thomas Weller
Thomas Weller

Reputation: 59279

Scope in Python is a bit different than in other languages like C++, C# or Java. In those languages, declaring

for (int i=0; i<10; i++) { ... }

i would only be defined in the scope of the loop. That's not the case for Python. i remains existent and has the last value it was assigned.

what if I want to access the first or second key? can I access with the same what I access the last one (without writing the key name or number)?

No. Except you make the loop stop at a different position.

Upvotes: 1

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