Simple Data Types Flashcards
VARIABLES
• What is a variable?
• What are the rules for naming a variable?
A variable is a label for a value you want to use in your program.
Variable names in Python follow two main rules:
• They must contain only letters, underscores, and numbers.
• They must start with a letter or underscore.
Good variable names are short but descriptive:
first name = 'albert' last_name = 'einstein' username = 'einsteina' age = 42
A variable can hold a small piece of information, or it can hold many gigabytes of data.
STRINGS
• What is a string?
• How do you store a string in a variable?
• How do you include tabs and newlines in a string?
A string is a value made up of one or more characters, surrounded by single or double quotes.
In this example, “I love Python!” is a string assigned to the variable message:
>>> message = "I love Python!" >>> print(message) I love Python!
Both single and double quotes work for strings, so you can use quotation marks inside a string:
>>> python_quote = 'I said, "I love Python!"' >>> print(python_quote) I said, "I love Python!"
Insert tabs and newlines into strings using the special sequences \t and \n:
>>> message = "Grocery list:\n\tmilk\n\teggs"
>>> print(message)
Grocery list:
milk
eggs
There is no limit on the length of a string.
STRING METHODS
• What is a string method?
• How do you change the case of a string?
• How do you strip whitespace from a string?
A string method is a function that performs an action on a string.
To change the case of a string, use the methods title(), upper (), and lower ():
>>> name = 'ella fitzgerald' >>> name.title() 'Ella Fitzgerald' >>> name.upper() 'ELLA FITZGERALD' >>> name = 'Ella Fitzgerald' >>> name.lower() 'ella fitzgerald'
The strip(), rstrip(), and strip() methods remove extra whitespace from strings, helpful for cleaning up data:
>>> name = ‘ jordan ’ >>> name.lstrip() ‘jordan ’ >>> name.rstrip() ‘ jordan' >>> name. strip() 'jordan'
String methods are useful for presenting data in a certain format or cleaning up user-submitted data.
USING VARIABLES IN STRINGS
• How do you insert the value from a variable into a string?
In Python, you can use a variable directly inside a string:
>>> username = 'efermi'
>>> print(f"Welcome back, {username}!")
Welcome back, efermi!
The f is short for format and tells Python to insert the value of the variable listed in braces inside the string. This tells Python to format the string using the given variable’s value.
COMMENTS
• How do you include a comment in your code?
• When should you include comments?
A comment is a line of text that’s ignored by the Python interpreter. Comments allow you to leave notes for yourself or others inside a program.
Comments begin with a hash mark:
# Greet the user.
username = 'adrian'
print (f"Welcome back {username}!")
Comments are useful when writing complex code that you might need to return to. They can remind you of the reasoning behind the logic.
Clear, concise comments are a sign of a professional programmer. When considering different ways to solve a specific problem, include a comment that explains the approach you chose to take.
NUMERICAL DATA
• What are the two main types of numerical data?
• How do you find out what type of data you’re working with?
• How do you convert between the two numerical types?
An intege , or int, is a number that doesn’t have a decimal point. A float is a number that does.
The type() function identifies the data type of its argument.
>>> type(3) <class 'int'> >>> type(3.5) <class 'float'>
The float () function converts an integer to a float:
>>> float(3) 3.0
Sometimes numerical information starts as a string. The float () function converts properly formatted strings to floats:
>>> float('3.5')
3.5
The int() function converts floats to integers by dropping the number’s decimal portion, not by rounding:
>>> int (3.0) 3 >>> int(3.9) 3
The int() function also converts strings to integers:
>>> int('3')
3
