Introduction to Programming with Python: Glossary

Python programs are plain text files.

Use the Jupyter Notebook for editing and running Python.

The Notebook has Control 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.

In Jupyter Notebooks, the ? command will display the same result as help() in a separate panel, with formatted text.

The official Python documentation is a good reference to the core Python language.

Use variables to store values.

Use print to display values.

Variables persist between cells.

Variables must be created before they are used.

Python is case-sensitive.

Use meaningful variable names.

Variables can be used in calculations.

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.

A list stores many values in a single structure.

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

Lists are mutable: list 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.

Python uses 0-based indexing. The first index is zero, the second index is one, and so forth

Indexing beyond the end of the collection is an error.

Tuples are another type of collection, but unlike lists, tuples are immutable.

Use if condition to start a conditional statement, elif condition to provide additional tests, and else to provide a default.

The bodies of the branches of conditional statements must be indented.

Use == to test for equality.

X and Y is only true if both X and Y are true.

X or Y is true if either X or Y, or both, are true.

Zero, the empty string, and the empty list are considered false; all other numbers, strings, and lists are considered true.

True and False represent truth values.

A dictionary is a data structure similar to a list, but that uses keys instead of indexes.

Dictionaries are created with {}, instead of [] for lists, or () for tuples.

A dictionary key can be a string, a number, or any hashable object.

To retrieve a value for a specific key we use the method .get.

Check if a key exists in a given dictionary by using the in operator.

We can iterate over a dictionary using a for loop to get both keys and keys:values.

A set is an unordered collection of items. Every element is unique and immutable.

Sets can be used to perform mathematical set operations like union, intersection, symmetric difference.

Use for variable in sequence to process the elements of a sequence one at a time.

The body of a for loop must be indented.

Use len(thing) to determine the length of something that contains other values.

Use accumulator structures with a for loop to update the value of an existing variable

Files are opened with the open() function.

The open() function returns a file object.

Files need to be closed when they are no longer required by your program.

The close() method of the file object closes a file.

The with statement provides an elegant and safe way to automatically close your files.

Data can be read from text files a line at a time by the readline() file object method.

If you want to process each line of a text file in order, then iteration is useful.

Data can be written to a file with the write() file object method.

Patterns are common and repeatable recipes for common problems. The text file sequential processing pattern is simple, robust and efficient.

Modules are simply Python files.

To use code from a module, it has to be imported.

The import command is used to import code from a module.

There are different ways to import from a module. Select the appropriate method based on the required effect.

Syntax errors occur because of illegal language constructs. They are detected by the Python parser.

Sometimes the actual error occurs slightly before the location reported by the Python exception.

Runtime errors occur when something goes wrong while a program is executing.

In Python, run-time errors raise exceptions.

Indentation is meaningful in Python.

Don’t repeat yourself. Keep your code DRY by using functions.

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 the function call are matched to the parameters in the function definition.

Optional arguments have a default value in the function definition.

Functions return results with the return statement.

Functions without explicit return values return None.

Within a function, print communicates with humans, return communicates with the computer.

Use docstrings to document your functions in a standard way.

Functions operate on input data, producing output data

Identifying and describing the data task is the biggest challenge in writing functions

A systematic design recipe will help you write elegant functions from the get-go!

Legal Python code follows rules of syntax

A Python keyword is a symbol that has special meaning in a Python script

Python provides for single and multiple line comments

An identifier names a value, e.g. as in the assignment statement: x = 21

A Python script consists of a sequence of statements that make use of keywords, identifiers and expressions

Indentation introduces a code block

[ and ] are used to surround literal list values

{ and } are used to surround literal dictionary values

( and ) are used for function parameters, to change expression evaluation order, and to specify tuple values

The PEP 8 Python Style Guidelines provide more code layout and convention details