Local Variable "age" referenced before assignment

Question

I recently started learning python. And im working on a problem.

class Person:
    age = 0
    def __init__(self,initial_Age):
        if initial_Age<0:
            age=0
            print("This person is not valid, setting age to 0.")
        else:
            age = initial_Age

    def amIOld(self):
        if(age<13):
            print("You are young.")
        elif(age>=13 and age<18):
            print("You are a teenager.")
        else:
            print("You are old.")
    def yearPasses(self):
        age = age + 1
T=int(input())
for i in range(0,T):
age=int(input())         
p=Person(age)  
p.amIOld()
for j in range(0,3):
    p.yearPasses();        
p.amIOld();
print ("")

The error I get is displayed below:

Traceback (most recent call last):
File "solution.py", line 27, in <module>
p.yearPasses();        
File "solution.py", line 19, in yearPasses
age = age + 1 
UnboundLocalError: local variable 'age' referenced before assignment

The Input for this goes like:

4(Number of test cases)
-1
10
16
18

The output has to be something like this:

This person is not valid, setting age to 0.
You are young.
You are young.

You are young.
You are a teenager.

You are a teenager.
You are old.

You are old.
You are old.

Can you please guide me to what Im doing wrong?. Thanks

Sidenote (I think it can be useful since you are learning): put more attention to the code style, check [the style guide](https://www.python.org/dev/peps/pep-0008/). For example, use `initial_age` instead of `initial_Age`, use camel cased method names (`am_i_old`, `year_passed`), no need to add ';' at the end of line, don't use short variables like `T` and `p`. — Borys Serebrov, Jan 20 '16 at 19:27

score 8 · Accepted Answer · answered Jan 20 '16 at 19:20

In python you have to use explicitly self to access instance attributes:

class Person:
    def __init__(self, initial_Age):
        if initial_Age < 0:
            self.age = 0
            print("This person is not valid, setting age to 0.")
        else:
            self.age = initial_Age

    def amIOld(self):
        if self.age<13:
            print("You are young.")
        elif self.age>=13 and self.age<18:
            print("You are a teenager.")
        else:
            print("You are old.")

    def yearPasses(self):
        self.age += 1

score 0 · Answer 2 · answered Mar 25 '21 at 04:34

In python you have to use explicitly self to access attributes from instance methods similar to 'this' in java

class Person:
def __init__(self,initialAge):
    # Add some more code to run some checks on initialAge
    self.initialAge = initialAge
    if initialAge < 0:
        print("Age is not valid, setting age to 0.")
    initialAge == 0 

def amIOld(self):
    # Do some computations in here and print out the correct statement to the console
    if self.initialAge<13:
        print("You are young.")
    elif self.initialAge>=13 and self.initialAge<18:
        print("You are a teenager.")
    elif self.initialAge>17:
        print("You are old.")

def yearPasses(self):
# Increment the age of the person in here
    self.initialAge += 1
    #print("age incrememted")

t = int(input())
for i in range(0, t):
age = int(input())         
p = Person(age)  
p.amIOld()
for j in range(0, 3):
    p.yearPasses()       
p.amIOld()
print("")

Local Variable "age" referenced before assignment

2 Answers2