CODEWITHSUNDEEP
pythonpython-2.7class
user13586124
user13586124

Reputation: 15

"none" appearing in classes

I am trying to learn classes and I don't understand why my code is printing "none"?


CODE

  def __init__(self, name, age):
    self.name = name
    self.age = age

  def introduce(self):
    print("Hello my name is " + self.name +" and I am "+ str(self.age) +" years old.")
  
  def crazy_talk(self):
    print(self.name +" says I'm a test")


p1 = Person("John", 36)
p2 = Person("Bob", 23)
p3 = Person("Joe", 3)
p4 = Person("John", 17)
p5 = Person("Ronald", 102)
p6 = Person("Kevin", 55)
p7 = Person("Albert", 70)

people_list=[p1,p2,p3,p4,p5,p6,p7]

for human in people_list:<br>
  print human.introduce()

OUTPUT

Hello my name is John and I am 36 years old.
None
Hello my name is Bob and I am 23 years old.
None
Hello my name is Joe and I am 3 years old.
None
Hello my name is John and I am 17 years old.
None
Hello my name is Ronald and I am 102 years old.
None
Hello my name is Kevin and I am 55 years old.
None
Hello my name is Albert and I am 70 years old.
None

Upvotes: 0

Views: 1000

Answers (2)

Ethan McCue
Ethan McCue

Reputation: 988

So, that expression human.introduce(), it doesn't return anything.

def introduce(self):
    print("Hello my name is " + self.name +" and I am "+ str(self.age) +" years old.")

This method definition says that, when called, that string will be printed out, but it does not actually return any value to the caller of the method, hence None.

So here, where you call the method

for human in people_list:
     print human.introduce()

For every human you call the method which will print out the string, and then the method will implicitly return None to the caller. This None is what the print inside of the for loop receives.

If you want the call to human.introduce() to return a string that can be printed, then you can change it to this

def introduce(self):
    return "Hello my name is " + self.name +" and I am "+ str(self.age) +" years old."

Which will not perform the side effect of printing the string, but it will return the string to the caller.

(Also for your own good, please transition to learning python 3 if at all possible. Python 2.7 is more than a decade old and is no longer supported)

Upvotes: 1

Jeen Broekstra
Jeen Broekstra

Reputation: 22042

This happens because on your last line you are printing out the return value of calling the human.introduce() method. This is always None. The introduce method itself prints out the the introduction text, but then returns no return value.

To fix, change your last line to just human.introduce(). Or alternatively, change your introduce() method to return (but not print) the text, and then print the result of calling the introduce() method on your last line.

Upvotes: 1

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