INF1-IP: Week 2

Lecture 2 - Strings and numbers

 

Learning outcomes
  • Distinguishing int, float, and str values and inspecting them with type()
  • Converting user input with int(), float(), and str()
  • Using floor division, remainder, exponentiation, and compound assignment
  • Combining strings and producing readable output with f-strings
  • Diagnosing common type and conversion errors

 

Key terms
Click to expand.

Type

The label assigned to values denoting what kind of values they are. Different types have different functionalities attached to them.

Type conversion

Changing a value from one type to another.

Integer

A type of value that represents a whole number.

Float

A type of value that represents numbers that can have a fractional part.

String

A type of value that represents text.

Operator

A symbol that performs an action on one or more values (its operands). May perform different actions depending on its operands' types.

Operand

The values that an operator acts on (e.g. the '2' and '3' in '2 + 3').

Compound assignment

A single operation that changes a value and updates the name that pointed to the old value to the new one.

String concatenation

Merging two strings together.

String interpolation

Evaluating variables and expressions directly inside of a formatted string.

 

New syntax
Click to expand.

type()

Returns what type a value is in the format <class 'type'>.

int(), float(), and str()

Functions to convert a value to an integer, float, and string, respectively. Only work if their arguments actually can be converted to the new type.

+ (on strings)

Concatenates strings.

* (on a string and an integer n)

Repeats the string n times.

//

Floor division: divides and rounds the quotient down. With two integer operands the result is an integer; with one or more float operands the result is a float.

%

Remainder: returns what is left over after floor division. With two integer operands the result is an integer; with one or more float operands the result is a float.

**

Exponentiation: raises a number to a power.

+=, -=, *=, /=, //=, %=, **=

Compound assignment operators: shorthands that change the value by a set amount and update the name to point to the new value in one go.

.upper() and .lower()

Transform a string to uppercase or lowercase characters, respectively.

.replace(old, new)

Searches a string and replaces the substring 'old' with 'new'.

f'...' and f"..."

Denotes a formatted string (or f-string). Inside the f-string, variables may be interpolated using {...} and formatted using modifiers.

TypeError

A type of error raised when an operation or function receives a value of an unsuitable type, such as adding a string and an integer together.

ValueError

A type of error raised when an operation accepts the argument's type but its particular value is unsuitable. For example, int("4.5") accepts a string argument, so there is no reason for a TypeError, but as the string does not represent a whole number, we run into a ValueError instead.

 

Further practice

 

 

Lecture 3 - Conditions and logic

 

Learning outcomes
  • Constructing comparisons with ==, !=, <, <=, >, and >=
  • Combining conditions with and, or, and not
  • Selecting one or more paths with if, elif, and else
  • Using indentation to show which statements belong to a branch
  • Recognising reserved keywords in Python

 

Key terms
Click to expand.

Boolean

A type of value that is either true or false.

Indentation

Whitespace at the beginning of lines of code that, in Python, groups pieces of code together.

Boundary test

When writing an if statement using numbers, a test that checks the statement by using values that are on the boundaries of the conditions.

Lexicographic comparison

Comparing strings from left to right using their code points.

Code point

A number assigned to a character so computers can process it.

Unicode

A common standard for code points, used by almost all computers.

Reserved keyword

A word with special functionality in Python that cannot be used as a variable name.

 

New syntax
Click to expand.

True and False

Boolean values in Python. Remember to capitalise them!

bool and bool()

The Boolean type in Python and the function to convert a value to the bool type in Python, respectively.

== and !=

Equal to and not equal to comparison operators. Work across types.

<, <=, >, >=

Less than; less than or equal to; greater than; and greater than or equal to comparison operators. Only work when their operands are of similar types.

and and or

Logical operators that combine conditions. Return a Boolean when their operands are Booleans; return one of their operands when they are not.

not

Logical operator that reverses a condition. Always returns a Boolean.

if, elif, else

Keywords that define if statements and their branches. Remember that for each branch, the head ends with a colon and the body is indented.

SyntaxError

A type of error that highlights when you break the rules of Python, such as naming a variable after a reserved keyword or attempting to assign a variable as part of a condition (by using = instead of ==, for example).

IndentationError

A type of error that highlights when you misuse indentation.

 

Further practice

 

 

Tutorial

Tutorial 1: The Tools of the Trade has you install Python and VS Code on your own laptop so you can start writing Python files outside of Jupyter notebooks.

  • Interactive notebook (right-click → Save As... then remove the .txt part so it is saved as an .ipynb)
    • Note that this notebook was created to be used in Notable; its interactive checker cells might not work in every environment.

 

Key terms
Click to expand.

Python interpreter

The program that reads and executes Python code.

Python source file

A text file containing Python code, normally with a .py filename extension.

Code editor

A program for creating and editing source files, such as IDLE or VS Code.

Extension

An add-on that gives an editor extra features, such as Python support in VS Code.

Terminal

A window or panel for text input and output; it commonly hosts a command shell, and can be both its own app or a part of another app (such as VS Code).

Command shell

A program that interprets commands to the operating system, such as starting other programs. Examples include PowerShell (on Windows), zsh (on macOS), or bash (on Linux).

Python interactive shell

An interface, recognised by the >>> prompt, for sending commands directly to the Python interpreter. Opened by running python (on Windows) or python3 in a command shell, or directly by opening the Python interpreter program or the IDLE Shell.

REPL

The Read–Evaluate–Print Loop followed by an interactive shell.

 

 

Assessment

No assessment this week.

 

 

License
All rights reserved The University of Edinburgh