Python notes 01

Variables are used to store values

Example: age = 23

Integer 23 is stored in the Variable age

A string is a series of characters, surrounded by single or double quotes.

Concatenation is the combining of strings.

• - first_name = 'albert'
• - last_name = 'einstein'
• - full_name = first_name + ' ' + last_name
• - print(full_name)

>>>albert einstein

• - Strings
• - Numbers (integer, floats, complex)
• - Boolean
• - Lists
• - Tuple
• - Dictionaries
• - Set

Variable names can contain only letters, numbers, and underscores.

They can start with a letter or an underscore, but not with a number. For instance, you can call a variable message_1 but not 1_message.

Spaces are not allowed in variable names, but underscores can be used to separate words in variable names. For example, greeting_message works, but greeting message will cause errors.

Python is case-sensetive, as such:

message = "Hello."

Message = "Hello, to you."

These are two different variables, that when called will give differing values.

A record of where the interpreter ran into trouble when trying to execute your code.

The title() method modifies the string by capitalizing the first letter of every word in a string.

• string = "jOeY mArLeY"
• print(string.title())
• >>>"Joey Marley"

Notes left within the code the are not processed.

Left as reminder/explanations for the code

In Python strings, the backslash " \ " is a special character which invokes an alternative interpretation on subsequent characters in a character sequence.

Example: string = ‘I don\’t love Mondays.’ # apostrophe can be used without issue due to the escape character

Examples of Escape Sequences ( \n ) and ( \t ).

Logical lines within the program

Two (2) statements:

• x = 3   # Statement number 1
• print(x)  # Statement number 2

Changes the case of a character (letter) in a string.

From lowercase to uppercase.

If letter is already uppercase, no effect.

Changes the case of a character (letter) in a string.

From uppercase to lowercase.

If letter is already lowercase, no effect.

Data that always represents itself

• Example: Integer 5 is always 5
• It does not contain data/information regarding another

• Strings are the same
• Example: "Hello world"

A list is a collection of items in a particular order.

In Python, square brackets ( [] ) indicate a list, and individual elements in the list are separated by commas.

Items in the List are indexed starting from zero (0, 1, 2, 3) and left to right.

Example: list = [‘car’, ‘boat’, ‘plane’, ‘train’]

NOTE: Use plural names for lists, to make your code easier to read.

Individual elements in a list are accessed according to their position, called the index.

The index of the first element is 0, the index of the second element is 1, and so forth. Negative indices refer to items at the end of the list.

To get a particular element, write the name of the list and then the index of the element in square brackets.

users = ['val', 'bob', 'mia', 'ron', 'ned']

• Getting the first element:
• first_user = users[0]
• >>>print(first_user)
• >>>'val'

• Getting the second element:
• second_user = users[1]
• >>>print(second_user)
• >>>'bob'

• Getting the last element:
• newest_user = users[-1]
• >>>print(newest_user)
• >>>'ned'

The IF statement is a test for particular conditions.

Example:

• if test expression:
•     statements()