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Python Python Basics All Together Now Gather Information

MICHAEL FOWLER
MICHAEL FOWLER
921 Points

Formatting Variables & ints

Two Questions:

  1. Why do we need to format variables? Example:
# Gather the user's name and assign it to a new variable
name = input("What is your name?   ")

 # Prompt the user by name and ask how many tickets they would like
num_tickets = input("How many tickets would you like, {}?   ".format(name))

My question is, why do I need to format the variable name? Is there reason why I simply cannot type "name" in the second question instead of using the placeholder for name and then the .format(name)?

  1. Similar questions with ints

Example:

# Prompt the user by name and ask how many tickets they would like
num_tickets = input("How many tickets would you like, {}?   ".format(name))
num_tickets = int(num_tickets)

Why do I need to turn the num_tickets into an int? Does Python not read num_tickets as an integer when it initially prompts the user?

Thank you!

[MOD - added ```python formatting -cf]

4 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,227 Points

Hi Michael! You may be misinterpreting the purpose of the string method format().

In the line:

num_tickets = input("How many tickets would you like, {}?   ".format(name))

it is the string "How many tickets would you like, {}" that is getting formatted by inserting the string held in the variable name into the placeholder {}.

This could be done without using the string format method. A concatenation version would look like:

num_tickets = input("How many tickets would you like, " + name + "?   ")

Using format() is not required. It is more of a coding style that many feel looks cleaner. Starting with Python3.6, there is also the new f string format:

num_tickets = input(f"How many tickets would you like, {name}?   ")

Post back if you have further questions. Good luck!!

MICHAEL FOWLER
MICHAEL FOWLER
921 Points

Hi Chris. Thanks you for clearing that up. I do see the difference now between the concatenation version and the other formatted examples and how it is a style preference.

Thanks for taking the time to answer..

Nick Moy
Nick Moy
1,061 Points

Hello, I was wondering why we have to reassign num_tickets = int(num_tickets) in order for python to recognize that math is being done here? Could someone help me better understand this logic?

Thanks!

Chris Freeman
Chris Freeman
Treehouse Moderator 68,227 Points

The goal is to get an integer value for the number of tickets assigned to the variable num_tickets based on input from the user. Since user input is received as a string, it will need to be converted using int(). But why use the form below, you ask?

num_tickets = int(num_tickets) 

The above line contains two steps:

  • take the object pointed to by num_tickets convert to an int, and return it.
  • reassign num_tickets to point to the object returned by the conversion

Keep in mind that num_tickets is just a label pointing to some object in memory. As illustrated below, the object id (what it’s pointing to) changes after the new assignment:

>>> num_tickets = '10'
>>> num_tickets
10
>>> id(num_tickets)
4584152120
>>> num_tickets = int(num_tickets)
>>> num_tickets
10
>>> id(num_tickets)
4344666944

The following code snippets produce the same results:

num_tickets = input("How many tickets would you like, {}?   ".format(name))
num_tickets = int(num_tickets)

str_tickets = input("How many tickets would you like, {}?   ".format(name))
num_tickets = int(str_tickets)

num_tickets = int(input("How many tickets would you like, {}?   ".format(name)))

Post back if you need more help. Good luck!!!

Nick Moy
Nick Moy
1,061 Points

That was very helpful! Thank you, Chris.