Chapter 2:
What happens when running Hello_World.py
print(“Hello Python world!”) –> input
Hello Python world! –> output
- .py = Python program, the editor runs the file through Python Interpreter which determines what each word means
- for example, print() prints whatever is inside the parentheses(not Python code), print is the name of the function
- syntax highlighting – displays different parts in different colors
Variables
- variable in Hello_World.py
message = “Hello Python world!” –> variable = value
print(message)
Hello Python world!
- can change the value of a variable at any time
Naming and using variables
- variable names can only contain letters, numbers, and underscores and can’t start with a number
- avoid using Python keywords and function names as variable names, for example, don’t use print
- lowercase “l” and uppercase “O” can be confused with 1 and 0
- at this stage, variables should be lowercase
Avoiding name errors when using variables
- Every programmer makes mistakes… print(mesage) –> name error
- traceback – a record of where the interpreter ran into trouble
Variables are labels
- labels you can assign to values or variable references a certain value
- Strings
- string – series of characters, anything inside single or double quotes
Changing case in a string with methods
Name.py
name = “ada lovelcae”
print(name.title())
Ada Lovelace
- Method – an action Python performs on a piece of data, followed by ()
- Dot(.) after name in name.title() tells Python to make the title() method act on the variable name
- title() method – title case
- upper() method – uppercase
- lower() method – lowercase, useful for storing data
Using variables in strings
- sometimes you’ll want to use a variable’s value inside a string
- for example, you might want to use two variables to represent a first name and a last name and then combine those values to display the full name
Full_Name.py
first_name = “ada”
last_name = “lovelace”
full_name = f”{first_name}{last_name}”
print(full_name)
ada lovelace
- place f before opening the quotation mark to insert a variable’s value into a string
- f-string – f is format, Python formats string by replacing the name of any variable in braces with its value
- use f-strings to compose complete messages like a sentence to greet users
first_name = “ada”
last_name = “lovelace”
full_name = f”{first_name}{last_name}”
print(f”Hello, {full_name.title()}!”)
Hello, Ada Lovelace!
- or
first_name = “ada”
last_name = “lovelace”
full_name = f”{first_name}{last_name}”
message = f”Hello, {full_name.title()}!”
print(message) –> cleaner print line
Hello, Ada Lovelace!
End of study session.