Having trouble with if/elif statements [duplicate]

Question 1

The following if test will always evaluate as true:

if animal=="Dog" or "dog":

To above works as if it had the parentheses:

if (animal=="Dog") or ("dog"):

The second part of the or will, under Python rules, always evaluate to True: non-empty strings have boolean value of True.

Here are three options that work:

if animal=="Dog" or animal == "dog":

if animal in ("Dog", "dog"):

if animal.lower() =="dog":

MORE: These issues can be easily tested on python's handy interactive command prompt. For example, observe the boolean value of "Dog" and "":

>>> bool("Dog"), bool("")
(True, False)

And, here is the combined statement:

>>> bool('Cat' == 'Dog' or 'dog')
True

Question 2

In python, all no empty string is evaluated as true, as:

if "something":
    print("True")
else
    print("False")

will always print True

So you need to set your if like:

if animal=="Dog" or animal=="dog":
    #Do something with dog
elif animal=="Cat" or animal=="cat":
    #Do something with cat
else:
    #Do something else

Question 3

You will want to edit your code as such:

import time
import sys

animal=input("What animal do you want to calculate the age of? - Possible choices: Cat/Dog")

if animal=="Dog"or animal=="dog":
    age=int(input("How old is your Dog?"))
    if age==1:
        print("Calculating the age of the Dog...")
        time.sleep(1)
        print("The age of the animal is: 11")
    elif age==2:
        print("Calculating the age of the Dog...")
        time.sleep(1)
        print("The age of the animal is: 11")
    else:
        age=age-2
        print("Calculating the age of the Dog...")
        time.sleep(1)
        agecalculation=age*4+22
        print("The age of the animal is:",agecalculation)
        time.sleep(2)
        print("End of program.")
        time.sleep(2)
        sys.exit()

elif animal=="Cat"or animal == "cat":
    age=int(input("How old is your Cat?"))
    if age==1:
        print("Calculating the age of the Cat...")
        time.sleep(1)
        print("The age of the animal is: 15")
    elif age==2:
        print("Calculating the age of the Cat...")
        time.sleep(1)
        print("The age of the animal is: 25")
    else:
        age=age-2
        print("Calculating the age of the Cat...")
        time.sleep(1)
        agecalculation=age*4+25
        print("The age of the animal is:",agecalculation)
        time.sleep(2)
        print("End of program.")
        time.sleep(2)
        sys.exit()
else:
    print("That is not an animal, or isn't on the list specified")
    animal=input("What animal do you want to calculate the age of? - Possible choices: Cat/Dog")

When you do if animal == "Dog" or "dog", it is evaluating if animal == "Dog", and if "dog". You could use animal.lower() == "dog", or use the edited code above.

Question 4

The obvious error has already been pointed out by pasztorpisti:

animal=='Cat'or'cat' is not what you wanted. Either use animal.lower()=='cat' or animal in ['cat', 'Cat'] or another approach.

I also think that your whole code could be trimmed down quite a bit. Maybe you can grab one or two ideas from the following snippet:

def dogAge(age):
    return 11 if age < 3 else age * 4 + 14

def catAge(age):
    if age == 1: return 15
    if age == 2: return 25
    return age * 4 + 17

animal = input("What animal do you want to calculate the age of? - Possible choices: Cat/Dog").lower()
if animal not in ['cat', 'dog']:
    print("That is not an animal, or isn't on the list specified")
    sys.exit(0)

age = int(input("How old is your {}?".format(animal)))

animalAge = {'cat': catAge, 'dog': dogAge}[animal](age)

print("The age of the animal is {}.".format(animalAge))

Question 5

I suspect (without having checked it) that the problem isn't your logic but your conditions.

animal == "Dog" or "dog" evaluates as (animal == "Dog") or "dog" which will always evaluate to True since "dog" is a non-null string. Try instead animal == "Dog" or animal == "dog", or better still what about animal in ("Dog", "dog") or animal.lower() == "dog"?