Printing a variable based on an input + another variable

Question

So I am trying to learn python at the moment. I'm a beginner programmer with only experience in limited web design and CMS administration.

I decided to create a simple little program that asked the user for the car number of a NASCAR team. Each team had a set of variables associated with it. So far, I did #1 and #2 and wanted to test the action of the code before completing the rest.

I ran into a problem where I believe I must be thinking about it wrong or maybe I am missing the knowledge because I just started learning to code in language.

Basically, it asks them for a car number and when they put it in, it display "driver(car number)" so if I input "2", it displays "driver2". But I want it to call the other variable driver2 instead which would display "Brad Keselowski" if correctly done.

Here's my code:

# NASCAR Numbers
# Display Driver Information Based on your Car Number Input

print("\t\t\tWelcome to NASCAR Numbers!")
print("\t\t Match Car Numbers to the Driver Names.")
input("\nPress the Enter Key to Play")

# 1 - Jamie McMurray
carnumber1 = ("1")
driver1 = ("Jamie McMurray")
make1 = ("Chevrolet")
sponsor1 = ("Bass Pro Shops/Allstate")
# 2 - Brad Keselowski
carnumber2 = ("2")
driver2 = ("Brad Keselowski")
make2 = ("Dodge")
sponsor2 = ("Miller Lite")

inputnumber = input("\nWhat car number do you want to lookup?\n\nCar Number:\t#")
driver = "driver"
print(driver + inputnumber)

Can anyone lead me in the right direction?

kojiro · Accepted Answer · 2012-05-30 21:09:43Z

3

You're not taking advantage of essential data structures. Whenever you want to map one value to another, you probably want a dictionary. Whenever you have a sequential list of items, you want a list.

>>> # NASCAR Numbers
... # Display Driver Information Based on your Car Number Input
... 
>>> print("\t\t\tWelcome to NASCAR Numbers!")
            Welcome to NASCAR Numbers!
>>> print("\t\t Match Car Numbers to the Driver Names.")
         Match Car Numbers to the Driver Names.
>>> cars = [] # Use a list to store the car information.
>>> cars.append({'driver': 'Jamie McMurray', 'make': 'Chevrolet', 'sponsor': 'Bass Pro Shops/Allstate'}) # Each individual car detail should be in a dictionary for easy lookup.
>>> cars.append({'driver': 'Brad Keselowski', 'make': 'Dodge', 'sponsor': 'Miller Lite'})
>>> inputnumber = input("\nWhat car number do you want to lookup?\n\nCar Number:\t#")

What car number do you want to lookup?

Car Number: #2
>>> driver = cars[inputnumber-1]['driver'] # Python lists start at zero, so subtract one from input.
>>> print("driver" + str(inputnumber))
driver2
>>> print(driver)
Brad Keselowski

By the way: Using input is dangerous, as whatever the user types is evaluated as python. Consider using raw_input, and then manually cast the input into an integer.

answered May 30, 2012 at 21:09

kojiro

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4 Comments

Hugh Bothwell Over a year ago

"input is dangerous" unless he's using Python 3

Steven Over a year ago

I'm concerned that none of the options seem to be working. Either your suggestion or the rest below. I'm currently running Python 3.1.

Hugh Bothwell Over a year ago

@Steven: Python 2 has a pair of functions, input() and raw_input(). input() tries to evaluate whatever is typed into it, so you can directly enter things like dictionaries; raw_input() just returns a string (hence "raw", as in "unevaluated"). Most people found that evaluating the input was unhelpful - if the input wasn't valid Python syntax, evaluating it would throw an error - so for Python 3 there is only input() which operates the same as Python 2's raw_input(). Hope that explains the problem!

Steven Over a year ago

Thanks Hugh. I will continue to learn and your explanation is very helpful.

Hugh Bothwell · Accepted Answer · 2012-05-31 00:44:45Z

Edits:

Added comments
Changed raw_input() to input() because he's using Python 3

.

# I create a class (a structure that stores data along with functions that
# operate on the data) to store information about each driver:
class Driver(object):
    def __init__(self, number, name, make, sponsor):
        self.number = number
        self.name = name
        self.make = make
        self.sponsor = sponsor

# Then I make a bunch of drivers, and store them in a list:
drivers = [
    Driver(1, "Jamie McMurray", "Chevrolet", "Bass Pro Shops/Allstate"),
    Driver(2, "Brad Keselowski", "Dodge", "Miller Lite")
]

# Then I use a comprehension (x for d in drivers) - it's kind of
# like a single-line for statement - to look at my list of drivers
# and create a dictionary so I can quickly look them up by driver number.
# It's a shorter way of writing:
#   number_index = {}  # an empty dictionary
#   for d in drivers:
#       number_index[d.number] = d
number_index = {d.number:d for d in drivers}

# Now I make a "main" function - this is a naming convention for
# "here's what I want this program to do" (the preceding stuff is
# just set-up):
def main():
    # show the welcome message
    print("\t\t\tWelcome to NASCAR Numbers!")
    print("\t\t Match Car Numbers to the Driver Names.")

    # loop forever
    # (it's not actually forever - when I want to quit, I call break to leave)
    while True:
        # prompt for input
        # get input from keyboard
        # strip off leading and trailing whitespace
        # save the result
        inp = input("\nEnter a car number (or 'exit' to quit):").strip()

        # done? leave the loop
        # .lower() makes the input lowercase, so the comparison works
        #   even if you typed in 'Exit' or 'EXIT'
        if inp.lower()=='exit':
            break

        try:
            # try to turn the input string into a number
            inp = int(inp)
        except ValueError:
            # int() didn't like the input string
            print("That wasn't a number!")

        try:
            # look up a driver by number (might fail)
            # then print a message about the driver
            print("Car #{} is driven by {}".format(inp, number_index[inp].name))
        except KeyError:
            # number[inp] doesn't exist
            print("I don't know any car #{}".format(inp))

# if this script is called directly by Python, run the main() function
# (if it is loaded as a module by another Python script, don't)
if __name__=="__main__":
    main()

This is pretty optimal code, but it could use some context for a "beginner programmer with only experience in limited web design and CMS administration".
Thanks to you both. I will study this code and want to tell you that I appreciate your time.

Maria Zverina · Accepted Answer · 2012-05-31 08:00:45Z

1

Try something like this:

from collections import namedtuple

Car = namedtuple('Car', 'driver make sponsor')


cars = [
        Car('Jim', 'Ford', 'Bass Pro Shops'),
        Car('Brad', 'Dodge', 'Miller Lite'),
        ]


inputnumber = input("\nWhat car number do you want to lookup?\n\nCar Number:\t#")
print(cars[int(inputnumber) - 1].driver)

edited May 31, 2012 at 8:00

answered May 30, 2012 at 21:13

Maria Zverina

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Comments

TryPyPy · Accepted Answer · 2012-05-30 21:34:08Z

To have the code working with the least changes, after changing input into raw_input twice, you can use this instead of print(driver + inputnumber):

 print(vars()[driver + inputnumber])

However, that's a rather bad way to do it: vars() gives you a dict of variables, so you should create a dict yourself, with the keys being the car numbers.

You can model each car/driver as one dictionary as follows:

# A dictionary to hold drivers
drivers = {}

# 1 - Jamie McMurray
jamie = {} # each driver modelled as a dictionary
jamie["carnumber"] = "1"
jamie["name"] = "Jamie McMurray"
jamie["make"] = "Chevrolet"
jamie["sponsor"] = "Bass Pro Shops/Allstate"

drivers[1] = jamie

# 2 - Brad Keselowski
brad = {}
brad["carnumber"] = "2"
brad["name"] = "Brad Keselowski"
brad["make"] = "Dodge"
brad["sponsor"] = "Miller Lite"

drivers[2] = brad

inputnumber = raw_input("\nWhat car number do you want to lookup?\n\nCar Number:\t#")

inputnumber = int(inputnumber) # Convert the string in inputnumber to an int

driver = drivers[inputnumber] # Fetch the corresponding driver from drivers

print(driver) # Print information, you can use a template to make it pretty

Soon, you'll realize that the natural way to model this is creating a class to represent a driver (and maybe other one to represent a car).

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