Programming in Python

Python programs are plain text files.

Use the Jupyter Notebook for editing and running Python.

The Notebook has Command and Edit modes.

Use the keyboard and mouse to select and edit cells.

The Notebook will turn Markdown into pretty-printed documentation.

Markdown does most of what HTML does.

Use variables to store values.

Use print to display values.

Variables persist between cells.

Variables must be created before they are used.

Variables can be used in calculations.

Use an index to get a single character from a string.

Use a slice to get a substring.

Use the built-in function len to find the length of a string.

Python is case-sensitive.

Use meaningful variable names.

Every value has a type.

Use the built-in function type to find the type of a value.

Types control what operations can be done on values.

Strings can be added and multiplied.

Strings have a length (but numbers don’t).

Must convert numbers to strings or vice versa when operating on them.

Can mix integers and floats freely in operations.

Variables only change value when something is assigned to them.

Use comments to add documentation to programs.

A function may take zero or more arguments.

Commonly-used built-in functions include max, min, and round.

Functions may only work for certain (combinations of) arguments.

Functions may have default values for some arguments.

Use the built-in function help to get help for a function.

The Jupyter Notebook has two ways to get help.

Every function returns something.

Python reports a syntax error when it can’t understand the source of a program.

Python reports a runtime error when something goes wrong while a program is executing.

Fix syntax errors by reading the source code, and runtime errors by tracing the program’s execution.

A list stores many values in a single structure.

Use an item’s index to fetch it from a list.

Lists’ values can be replaced by assigning to them.

Appending items to a list lengthens it.

Use del to remove items from a list entirely.

The empty list contains no values.

Lists may contain values of different types.

Character strings can be indexed like lists.

Character strings are immutable.

Indexing beyond the end of the collection is an error.

A for loop executes commands once for each value in a collection.

The first line of the for loop must end with a colon, and the body must be indented.

Indentation is always meaningful in Python.

A for loop is made up of a collection, a loop variable, and a body.

Loop variables can be called anything (but it is strongly advised to have a meaningful name to the looping variable).

The body of a loop can contain many statements.

Use range to iterate over a sequence of numbers.

The Accumulator pattern turns many values into one.

Use if statements to control whether or not a block of code is executed.

Conditionals are often used inside loops.

Use else to execute a block of code when an if condition is not true.

Use elif to specify additional tests.

Conditions are tested once, in order.

Create a table showing variables’ values to trace a program’s execution.

Most of the power of a programming language is in its libraries.

A program must import a library module in order to use it.

Use help to learn about the contents of a library module.

Import specific items from a library to shorten programs.

Create an alias for a library when importing it to shorten programs.

Break programs down into functions to make them easier to understand.

Define a function using def with a name, parameters, and a block of code.

Defining a function does not run it.

Arguments in call are matched to parameters in definition.

Functions may return a result to their caller using return.

The scope of a variable is the part of a program that can ‘see’ that variable.

Use the numpy library to work with arrays in Python.

The expression array.shape gives the shape of an array.

Use array[x, y] to select a single element from a 2D array.

Array indices start at 0, not 1.

All the indexing and slicing that we’ve used on lists and strings also works on arrays.

Use low:high to specify a slice that includes indices from low to high-1.

Use numpy.mean(array), numpy.max(array), and numpy.min(array) to calculate simple statistics.

Use numpy.mean(array, axis=0) or numpy.mean(array, axis=1) to calculate statistics across the specified axis.

Use the pyplot library from matplotlib for creating simple visualizations.

Many styles of plot are available: see the Python Graph Gallery for more options.

Use a for loop to process files given a list of their names.

Use glob.glob(pattern) to create a list of files whose names match a pattern.

Use * in a pattern to match zero or more characters, and ? to match any single character.

Use glob and for to process batches of files.

Follow standard Python style in your code.

Use docstrings to provide online help.

Python supports a large community within and outwith research.

We are constantly seeking to improve this course.