Week-3-1

Types in Python

• Types represent various ways of representing data in Python.

  • Example: Integer is a type.

  • We will focus on Strings in this discussion.

Strings

• Definition: A string is a sequence of characters.

  • Characters can be numbers, letters, or symbols placed one after another.

  • Used for defining names, identifiers, and any textual representation.

• String Literals: A sequence of characters enclosed in single (' ') or double (" ") quotes.

  • There is no distinction between single and double quotes in Python as long as consistency is maintained.

• String as a Sequence Type: Strings are a sequence type, meaning you can access characters by their position.

  • Example: The string "Trish" has characters indexed starting from zero (T=0, r=1, i=2, s=3, h=4).

String Indexing

• Zero-Based Indexing: Indexing in Python starts at zero.

• Visualization:

  • For the string "Trish":

    • Indexes: 0 - T, 1 - r, 2 - i, 3 - s, 4 - h.

Working with Strings: Exercises

• Filling in Blanks Exercise:

  • Create sentences by substituting placeholders with input values (e.g., relative, food).

    • Example sentence: "My aunt says eating chile will make one excellent."

• Input: Use the input() function to get user inputs to replace placeholders.

• Print Statement:

  • Use print() to output the final string with values substituted:

    • Separated by commas for literals and variables.

Finding Length of Strings

• Using len() Function:

  • Calculates the length of a string.

  • Example: len("George V") returns the length of the string as an integer.

• Backslash as Continuation Character:

  • Allows splitting strings across multiple lines.

    • Example: George_V = "George \ V" creates a single string.

Individual Character Access

• Access characters via square brackets [] based on their index.

• Positive Indexing:

  • alphabet[0] returns 'A', alphabet[1] returns 'B', etc.

• Negative Indexing:

  • alphabet[-1] returns the last character, alphabet[-2] the second last, and so forth.

String Mutability

• Strings are immutable: Individual characters cannot be changed.

• Example of Error: Attempting to assign a new character to a specific index will cause an error.

String Concatenation

• Using + Operator:

  • Combines two strings.

  • Example: "Mars" + " has " results in "Mars has".

Formatting Strings

• Formatted Strings:

  • Begin with the letter 'F' followed by quotes. Variable placeholders are included in curly braces {}.

• Example: f"Val: {value}" replaces {value} with the actual value.

• Placeholder Expressions: Formatting can also evaluate expressions with the equal sign in formatted strings.

Lists

• Definition: A list is a container that holds multiple items.

  • Created using square brackets [], and items are separated by commas.

• Example: prices = ['$20', 3.0, 5] is a list with elements of different types.

Accessing List Elements

• Indexing in Lists: Similar to strings, accessing elements starts from index 0.

• Updating List Values: Unlike strings, elements in lists can be modified.

List Methods and Functions

• Common Methods:

  • append(): Adds a new element to the end of the list.

  • pop(): Removes an element by index and returns its value.

  • remove(): Removes an element by value and does not return anything.

• Sequence Type Methods: Functions that operate on sequence types include len(), min(), max(), sum(), etc.

• Concatenation of Lists: Two lists can be combined by using the + operator, effectively joining them into a new list.