Codecademy Learn Python 3

static method

methods that are not attached to any individual object. invoked on the class itself. method without the self keyword.

NameError

A NameError is reported by the Python interpreter when it detects a variable that is unknown. This can occur when a variable is used before it has been assigned a value or if a variable name is spelled differently than the point at which it was defined. The Python interpreter will display the line of code where the NameError was detected and indicate which name it found that was not defined.

Syntax Error

A SyntaxError is reported by the Python interpreter when some portion of the code is incorrect. This can include misspelled keywords, missing or too many brackets or parenthesis, incorrect operators, missing or too many quotation marks, or other conditions.

SyntaxError

A SyntaxError is reported by the Python interpreter when some portion of the code is incorrect. This can include misspelled keywords, missing or too many brackets or parenthesis, incorrect operators, missing or too many quotation marks, or other conditions.

ZeroDivisionError

A ZeroDivisionError is reported by the Python interpreter when it detects a division operation is being performed and the denominator (bottom number) is 0. In mathematics, dividing a number by zero has no defined value, so Python treats this as an error condition and will report a ZeroDivisionError and display the line of code where the division occurred. This can also happen if a variable is used as the denominator and its value has been set to or changed to 0.

Instantiation Vocab

A class doesn't accomplish anything simply by being defined. A class must be instantiated. In other words, we must create an instance of the class, in order to breathe life into the schematic. Instantiating a class looks a lot like calling a function. We would be able to create an instance of our defined CoolClass as follows:

Class Vocab

A class is a template for a data type. It describes the kinds of information that class will hold and how a programmer will interact with that data. Define a class using the class keyword. PEP 8 Style Guide for Python Code recommends capitalizing the names of classes to make them easier to identify.

Comments

A comment is a piece of text within a program that is not executed. It can be used to provide additional information to aid in understanding the code. The # character is used to start a comment and it continues until the end of the line.

Modulo Operator %

A modulo calculation returns the remainder of a division between the first and second number. For example: The result of the expression 4 % 2 would result in the value 0, because 4 is evenly divisible by 2 leaving no remainder. The result of the expression 7 % 3 would return 1, because 7 is not evenly divisible by 3, leaving a remainder of 1.

List Slicing

A slice, or sub-list of Python list elements can be selected from a list using a colon-separated starting and ending point. The syntax pattern is myList[START_NUMBER:END_NUMBER]. The slice will include the START_NUMBER index, and everything until but excluding the END_NUMBER item. When slicing a list, a new list is returned, so if the slice is saved and then altered, the original list remains the same.

Strings

A string is a sequence of characters (letters, numbers, whitespace or punctuation) enclosed by quotation marks. It can be enclosed using either the double quotation mark " or the single quotation mark '. If a string has to be broken into multiple lines, the backslash character \ can be used to indicate that the string continues on the next line.

Variables

A variable is used to store data that will be used by the program. This data can be a number, a string, a Boolean, a list or some other data type. Every variable has a name which can consist of letters, numbers, and the underscore character _. The equal sign = is used to assign a value to a variable. After the initial assignment is made, the value of a variable can be updated to new values as needed.

Integers

An integer is a number that can be written without a fractional part (no decimal). An integer can be a positive number, a negative number or the number 0 so long as there is no decimal portion. The number 0 represents an integer value but the same number written as 0.0 would represent a floating point number.

Integers Review Card

An integer is a number that can be written without a fractional part (no decimal). An integer can be a positive number, a negative number or the number 0 so long as there is no decimal portion. The number 0 represents an integer value but the same number written as 0.0 would represent a floating point number.

Boolean Values

Booleans are a data type in Python, much like integers, floats, and strings. However, booleans only have two values: True False Specifically, these two values are of the bool type. Since booleans are a data type, creating a variable that holds a boolean value is the same as with other data types.

Format of study cards

Cheatsheet terms with the review concepts image techniques and make technique cards

Section Card: Hello World CheatSheet

Comments Arithmetic Operations Plus-Equals Operator += Variables Modulo Operator % Integers String Concatenation Errors ZeroDivisionError Strings SyntaxError NameError Floating Point Numbers print() Function

__main__ Vocab or Function Note

In Python __main__ means "this current file that we're running"

Zero-Indexing

In Python, list index begins at zero and ends at the length of the list minus one. For example, in this list, 'Andy' is found at index 2.

Python Lists: Data Types

In Python, lists are a versatile data type that can contain multiple different data types within the same square brackets. The possible data types within a list include numbers, strings, other objects, and even other lists.

Lists

In Python, lists are ordered collections of items that allow for easy use of a set of data. List values are placed in between square brackets [ ], separated by commas. It is good practice to put a space between the comma and the next value. The values in a list do not need to be unique (the same value can be repeated). Empty lists do not contain any values within the square brackets.

Adding Lists Together

In Python, lists can be added to each other using the plus symbol +. As shown in the code block, this will result in a new list containing the same items in the same order with the first list's items coming first. Note: This will not work for adding one item at a time (use .append() method). In order to add one item, create a new list with a single value and then use the plus symbol to add the list.

Comparison Operators

In Python, relational operators compare two values or expressions. The most common ones are: < less than > greater than <= less than or equal to >= greater than or equal too If the relation is sound, then the entire expression will evaluate to True. If not, the expression evaluates to False.

List Method .append()

In Python, you can add values to the end of a list using the .append() method. This will place the object passed in as a new element at the very end of the list. Printing the list afterwards will visually show the appended value. This .append() method is not to be confused with returning an entirely new list with the passed object.

Accessing 2D Lists

In order to access elements in a 2D list, an index for the sublist and the index for the element of the sublist both need to be provided. The format for this is list[sublist_index][element_in_sublist_index].

Modifying 2D Lists

In order to modify elements in a 2D list, an index for the sublist and the index for the element of the sublist need to be provided. The format for this is list[sublist_index][element_in_sublist_index] = new_value.

Negative List Indices

Negative indices for lists in Python can be used to reference elements in relation to the end of a list. This can be used to access single list elements or as part of defining a list range. For instance: To select the last element, my_list[-1]. To select the last three elements, my_list[-3:]. To select everything except the last two elements, my_list[:-2].

Plus-Equals Operator += Review Card

Plus-Equals Operator +=

List Indices

Python list elements are ordered by index, a number referring to their placement in the list. List indices start at 0 and increment by one. To access a list element by index, square bracket notation is used: list[index].

Arithmetic Operations

Python supports different types of arithmetic operations that can be performed on literal numbers, variables, or some combination. The primary arithmetic operators are: + for addition - for subtraction * for multiplication / for division % for modulus (returns the remainder) ** for exponentiation

String Concatenation

Python supports the joining (concatenation) of strings together using the + operator. The + operator is also used for mathematical addition operations. If the parameters passed to the + operator are strings, then concatenation will be performed. If the parameter passed to + have different types, then Python will report an error condition. Multiple variables or literal strings can be joined together using the + operator.

Floating Point Numbers

Python variables can be assigned different types of data. One supported data type is the floating point number. A floating point number is a value that contains a decimal portion. It can be used to represent numbers that have fractional quantities. For example, a = 3/5 can not be represented as an integer, so the variable a is assigned a floating point value of 0.6.

List Method .pop()

The .pop() method allows us to remove an element from a list while also returning it. It accepts one optional input which is the index of the element to remove. If no index is provided, then the last element in the list will be removed and returned.

List Method .count()

The .count() Python list method searches a list for whatever search term it receives as an argument, then returns the number of matching entries found.

List Method .remove()

The .remove() method in Python is used to remove an element from a list by passing in the value of the element to be removed as an argument. In the case where two or more elements in the list have the same value, the first occurrence of the element is removed.

List Method .sort()

The .sort() Python list method will sort the contents of whatever list it is called on. Numerical lists will be sorted in ascending order, and lists of Strings will be sorted into alphabetical order. It modifies the original list, and has no return value.

not Operator

The Python Boolean not operator is used in a Boolean expression in order to evaluate the expression to its inverse value. If the original expression was True, including the not operator would make the expression False, and vice versa.

and Operator

The Python and operator performs a Boolean comparison between two Boolean values, variables, or expressions. If both sides of the operator evaluate to True then the and operator returns True. If either side (or both sides) evaluates to False, then the and operator returns False. A non-Boolean value (or variable that stores a value) will always evaluate to True when used with the and operator.

elif Statement

The Python elif statement allows for continued checks to be performed after an initial if statement. An elif statement differs from the else statement because another expression is provided to be checked, just as with the initial if statement. If the expression is True, the indented code following the elif is executed. If the expression evaluates to False, the code can continue to an optional else statement. Multiple elif statements can be used following an initial if to perform a series of checks. Once an elif expression evaluates to True, no further elif statements are executed.

else Statement

The Python else statement provides alternate code to execute if the expression in an if statement evaluates to False. The indented code for the if statement is executed if the expression evaluates to True. The indented code immediately following the else is executed only if the expression evaluates to False. To mark the end of the else block, the code must be unindented to the same level as the starting if line.

if Statement

The Python if statement is used to determine the execution of code based on the evaluation of a Boolean expression. If the if statement expression evaluates to True, then the indented code following the statement is executed. If the expression evaluates to False then the indented code following the if statement is skipped and the program executes the next line of code which is indented at the same level as the if statement.

Errors

The Python interpreter will report errors present in your code. For most error cases, the interpreter will display the line of code where the error was detected and place a caret character ^ under the portion of the code where the error was detected.

Determining the List Length with len()

The Python len() function can be used to determine the number of items found in the list it accepts as an argument.

List Method .insert()

The Python list method .insert() allows us to add an element to a specific index in a list. It takes in two inputs: The index that you want to insert into. The element that you want to insert at the specified index.

Not Equals Operator !=

The Python not equals operator, !=, is used to compare two values, variables or expressions to determine if they are NOT the same. If they are NOT the same, the operator returns True. If they are the same, then it returns False. The operator takes the data type into account when making the comparison so a value of 10 would NOT be equal to the string value "10" and the operator would return True. If expressions are used, then they are evaluated to a value of True or False before the comparison is made by the operator.

or Operator

The Python or operator combines two Boolean expressions and evaluates to True if at least one of the expressions returns True. Otherwise, if both expressions are False, then the entire expression evaluates to False.

sorted() Function

The Python sorted() function accepts a list as an argument, and will return a new, sorted list containing the same elements as the original. Numerical lists will be sorted in ascending order, and lists of Strings will be sorted into alphabetical order. It does not modify the original, unsorted list.

Instance Variables: Vocab

The data held by an object is referred to as an instance variable. Instance variables aren't shared by all instances of a class — they are variables that are specific to the object they are attached to.

Equal Operator ==

The equal operator, ==, is used to compare two values, variables or expressions to determine if they are the same. If the values being compared are the same, the operator returns True, otherwise it returns False. The operator takes the data type into account when making the comparison, so a string value of "2" is not considered the same as a numeric value of 2.

Plus-Equals Operator +=

The plus-equals operator += provides a convenient way to add a value to an existing variable and assign the new value back to the same variable. In the case where the variable and the value are strings, this operator performs string concatenation instead of addition. The operation is performed in-place, meaning that any other variable which points to the variable being updated will also be updated.

print() Function

The print() function is used to output text, numbers, or other printable information to the console. It takes one or more arguments and will output each of the arguments to the console separated by a space. If no arguments are provided, the print() function will output a blank line.

print(Function) Review Concepts

The print() function is used to output text, numbers, or other printable information to the console. It takes one or more arguments and will output each of the arguments to the console separated by a space. If no arguments are provided, the print() function will output a blank line.

override string methods to get data instead of a memory location

any time we override a string method we need to return a string https://www.youtube.com/watch?v=MikphENIrOo&t=1280s at 23:40 minutes

Classes technique

hyperlink: https://www.codecademy.com/courses/learn-python-3/lessons/data-types/exercises/self If you want to print out a calculation that has been performed by a class and its respective method... syntax: variable holding the object with its input. than put a period. than put the name of the method with closed parenthesis. see picture.

parameters vs arguments

parameters are used when using the contructor.(definition) arguements are used later when creating the object. (invocation)