Programming with Python: Glossary

Key Points

Running and Quitting	Use iPython for editing and running Python. Use the keyboard and mouse to select and edit cells.
Variables and Assignment	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.
Data Types and Type Conversion	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.
Lists	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.
Tuples & Dictionaries	A tuple is a list that can never be changed. Use an item’s index to fetch it from a tuple. Dictionaries are lists in which the semantic meaning of each entry is more important than its order. New entries can be added to an existing dictionary by assignment. Dictionary keys are unique - only one item can exist per key Use `del` to remove items from a list entirely You can access all the keys and all the values of a dictionary Collections (lists, tuples, dictionaries) may be nested arbitrarily Code clarity & maintainability should guide choice of collection type
For Loops	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.
Conditionals	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.
Creating Functions	Define a function using `def function_name(parameter)`. The body of a function must be indented. Call a function using `function_name(value)`. Numbers are stored as integers or floating-point numbers. Integer division produces the whole part of the answer (not the fractional part). Variables defined within a function can only be seen and used within the body of the function. If a variable is not defined within the function it is used, Python looks for a definition before the function call Use `help(thing)` to view help for something. Put code whose parameters change frequently in a function, then call it with different parameter values to customize its behavior.
Errors and Exceptions	Tracebacks can look intimidating, but they give us a lot of useful information about what went wrong in our program, including where the error occurred and what type of error it was. An error having to do with the ‘grammar’ or syntax of the program is called a `SyntaxError`. If the issue has to do with how the code is indented, then it will be called an `IndentationError`. A `NameError` will occur if you use a variable that has not been defined, either because you meant to use quotes around a string, you forgot to define the variable, or you just made a typo. Containers like lists and strings will generate errors if you try to access items in them that do not exist. This type of error is called an `IndexError`. Trying to read a file that does not exist will give you an `FileNotFoundError`. Trying to read a file that is open for writing, or writing to a file that is open for reading, will give you an `IOError`.
Live Coding Shielding Problem	Use Python to write a simple shielding calculation script. Learn some best practices when writing Python.

Glossary

additive color model: A way to represent colors as the sum of contributions from primary colors such as red, green, and blue.
argument: A value given to a function or program when it runs. The term is often used interchangeably (and inconsistently) with parameter.
assertion: An expression which is supposed to be true at a particular point in a program. Programmers typically put assertions in their code to check for errors; if the assertion fails (i.e., if the expression evaluates as false), the program halts and produces an error message. See also: invariant, precondition, postcondition.
assign: To give a value a name by associating a variable with it.
body: (of a function): the statements that are executed when a function runs.
call stack: A data structure inside a running program that keeps track of active function calls.
case-insensitive: Treating text as if upper and lower case characters of the same letter were the same. See also: case-sensitive.
case-sensitive: Treating text as if upper and lower case characters of the same letter are different. See also: case-insensitive.
comment: A remark in a program that is intended to help human readers understand what is going on, but is ignored by the computer. Comments in Python start with a # character and run to the end of the line;
compose: To apply one function to the result of another, such as f(g(x)).
conditional statement: A statement in a program that might or might not be executed depending on whether a test is true or false.
comma-separated values: (CSV) A common textual representation for tables in which the values in each row are separated by commas.
default value: A value to use for a parameter if nothing is specified explicitly.
defensive programming: The practice of writing programs that check their own operation to catch errors as early as possible.
delimiter: A character or characters used to separate individual values, such as the commas between columns in a CSV file.
documentation: Human-language text written to explain what software does, how it works, or how to use it.
empty string: A character string containing no characters, often thought of as the “zero” of text.
encapsulation: The practice of hiding something’s implementation details so that the rest of a program can worry about what it does rather than how it does it.
floating-point number: A number containing a fractional part and an exponent. See also: integer.
for loop: A loop that is executed once for each value in some kind of set, list, or range. See also: while loop.
function call: A use of a function in another piece of software.
in-place operators: An operator such as += that provides a shorthand notation for the common case in which the variable being assigned to is also an operand on the right hand side of the assignment. For example, the statement x += 3 means the same thing as x = x + 3.
index: A subscript that specifies the location of a single value in a collection, such as a single pixel in an image.
inner loop: A loop that is inside another loop. See also: outer loop.
integer: A whole number, such as -12343. See also: floating-point number.
invariant: An expression whose value doesn’t change during the execution of a program, typically used in an assertion. See also: precondition, postcondition.
library: A family of code units (functions, classes, variables) that implement a set of related tasks.
loop variable: The variable that keeps track of the progress of the loop.
outer loop: A loop that contains another loop. See also: inner loop.
parameter: A variable named in the function’s declaration that is used to hold a value passed into the call. The term is often used interchangeably (and inconsistently) with argument.
pipe: A connection from the output of one program to the input of another. When two or more programs are connected in this way, they are called a “pipeline”.
postcondition: A condition that a function (or other block of code) guarantees is true once it has finished running. Postconditions are often represented using assertions.
precondition: A condition that must be true in order for a function (or other block of code) to run correctly.
regression: To re-introduce a bug that was once fixed.
RGB: An additive model that represents colors as combinations of red, green, and blue. Each color’s value is typically in the range 0..255 (i.e., a one-byte integer).
shape: An array’s dimensions, represented as a vector. For example, a 5×3 array’s shape is (5,3).
silent failure: Failing without producing any warning messages. Silent failures are hard to detect and debug.
slice: A regular subsequence of a larger sequence, such as the first five elements or every second element.
stack frame: A data structure that provides storage for a function’s local variables. Each time a function is called, a new stack frame is created and put on the top of the call stack. When the function returns, the stack frame is discarded.
standard input: A process’s default input stream. In interactive command-line applications, it is typically connected to the keyboard; in a pipe, it receives data from the standard output of the preceding process.
standard output: A process’s default output stream. In interactive command-line applications, data sent to standard output is displayed on the screen; in a pipe, it is passed to the standard input of the next process.
string: Short for “character string”, a sequence of zero or more characters.
syntax error: CHECKME: a programming error that occurs when statements are in an order or contain characters not expected by the programming language
test oracle: A program, device, data set, or human being against which the results of a test can be compared.
test-driven development: The practice of writing unit tests before writing the code they test.
type: CHECKME The classification of something in a program (for example, the contents of a variable) as a kind of number (e.g. floating-point, integer), string, or something else.
while loop: A loop that keeps executing as long as some condition is true. See also: for loop.