Python Keywords, Concepts, Functions

See also Python Programming - Getting Started

Following are terse descriptions for Python3 keywords, programming concepts, and commonly used functions. For more information, see w3schools for a bit more explanation and python.org for the language reference.

Keywords

The following are heavily used in all levels of Python programming. This is a minimum set of keywords to know how to use.

• break - exit the current loop
• continue - in a loop, go to next iteration of the loop
• is - determine whether two objects are the same object (not just value)
• import, from - to load a module
• def - declare a function
• while - loop with only condition
• if, elif, else - conditional statements (three keywords)
• for - loop with that iterates through a list
• return - keyword to send a value back from a function
• and - boolean operator, True only if both sides are True
• or - boolean operator, True if either side is True
• not - boolean operator, negates
• True, False - boolean values (two keywords)
• del - remove from a list by position
• try, except - handle an exception, basic use (2 keywords)
• raise, assert - raise/indicate an exception (2 keywords)
• in - test if something is inside of a list/string/tuple/dictionary
• None - special value for a variable that has no value
• pass - empty statement that does not do anything

More Keywords

These keywords are often not introduced or heavily used until the second Python course.

• as, finally, with, else - exception handling, more keywords (4 keywords)
• class - defining new class data type (for object-oriented programming)
• lambda - create unnamed / anonymous function
• global, nonlocal - access variables outside of current scope (2 keywords)
• async, await - for writing asynchronous code with asynchio package (2 keywords)
• yield - for creating generator functions

Concepts

See this video for a demo and explanation of basic data types and variables.

These are terms that we use to describe programs. These are terms that have a precise meaning when talking about programs.

• string - text data type
• boolean - data type for True and False
• floating point - data type that stores numbers with fractional parts (e.g., 3.14 or 2.2)
• integer - data type that stores only integers
• None - a special value in Python that means "nothing" but is different than 0, False, and ""
• variable - name for a place in memory to store values. Two basic things you do with a variable - (i) store a value into the variable, (ii) get the value from the variable.
• keywords - also called reserved words - these are names that should not be used for variable names because they have special meaning to python. Example: for is used for loops and shouldn't be used as a variable name.
• function - also called procedures or methods - name for a block of code that does something and that your code can use when needed. Two basic things you can do with a function - (i) define what the function is (specify the code for the function), (ii) call the function later on in your code. Three main parts of defining function - (a) function code (called the body), (b) function parameters (aka input variables), (c) function return values. Three main parts of calling/using a function - (1) specify the arguments to the function (which are passed in to the parameters of the function), (2) call the function, (3) get the return value of the function.
• flow chart - diagram that shows the steps / flow of control in a program (also used to diagram decision-making in other settings - e.g., diagnosis of an illness, managing a factory, ...)
• binary operator - operator that takes two values to produce a result. An example is addition, 2 + 3 results in 5. Another example is == comparison, 'hi' == 'bye' results in False because the two are not equal.
• unary operator - operator that takes one value to produce a result. An example is Boolean not, not True results in False.
• operator precedence - rules for which operators are evaluated first in an expression. For example, in 1 + 2 * 3, the multiplication is performed first, giving 1 + 6, and then the + is performed to result in 7. For Python, see python.org.
• operator associativity - rule whether operators of the same type are evaluated left-to-right or right-to-left. Math operators are left-to-right. For Python, see python.org.

Commonly Used Functions

• print - function to write to the screen
• int, float, str - functions to convert to integer, floating point number, or string
• range - function to generate a sequence of numbers
• len - function to get the length of a string, list, or tuple