Python Programming
boolean expressions
A boolean expression is a statement that can either be True or False.
Boolean operators: AND
AND combines two boolean values and evaluates as True if both its components are True, but False otherwise. syntax: and True : True = True False : False = False True: False = False False: True = False
if statement
Allows statements to be conditionally executed or skipped over
else if statements
An elif statement checks another condition after the previous if statements conditions aren't met.
name error
an exception that occurs when Python is asked to produce a value for a variable that has not been assigned a value
lists
an ordered set of objects in Python begins and ends with brackets and individual items are separated with commas
positional arguments
arguments that are assigned based upon position when calling a function EX: function(argument1, argument2) the parameters will go to the parameter in each position (1 to position 1, 2 to position 2)
strings
blocks of text designated with " " or ' '
written understanding of nested for loops regarding lists inside of lists
called the outside list and iterate through the inside list then call the inside list and iterate through the data contained in the inside lists
final example of list comprehension
celsius = [0, 10, 15, 32, -5, 27, 3] fahrenheit = [degree * 9/5 + 32 for degree in celsius] print(fahrenheit) Brilliant!
string concatenation
combining multiple strings or variables for display as one message using the + operator between them (cannot take non-string variables)
# comment here
comments are designated with a # to ensure python ignores your text
continue as an element of loops
continue allows an iteration to be skipped if the continue function is used based upon conditions or a blanket use of it
str(variable)
converts the variable into a string and is very useful for string concatenation
list.count() function
counts how many times the selected item appears in a list syntax: listName.count(input)
default arguments for parameters
declaring what the argument will be by setting it in the function declaration def greet_customer(special_item, grocery_store="Engrossing Grocers"): print("Welcome to "+ grocery_store + ".") print("Our special is " + special_item + ".") print("Have fun shopping!") notice how grocery store was assigned a value
return example
def divide_by_four(input_number): return input_number/4
try and expect example
def divides(a,b): try: result = a / b print (result) except ZeroDivisionError: print ("Can't divide by zero!")
declaring a function
def function_name(): some code #the above 'some code' line would be indented
returning and collecting multiple values with functions
def get_boundaries(target, margin): low_limit = target - margin high_limit = margin + target return low_limit, high_limit low, high = get_boundaries(target = 100, margin = 20)
declaring a function example
def greet_customer(): print("Welcome to Engrossing Grocers.") print("Our special is mandarin oranges.") print("Have fun shopping!") greet_customer() # prints greeting lines
multiple parameters (separated by a comma)
def greet_customer(grocery_store, special_item): print("Welcome to "+ grocery_store + ".") print("Our special is " + special_item + ".") print("Have fun shopping!") greet_customer("Stu's Staples", "papayas")
parameter example
def greet_customer(special_item): print("Welcome to Engrossing Grocers.") print("Our special is " + special_item + ".") print("Have fun shopping!") special_item is an variable passed as an argument in the function
else statements
defines what happens for anything not included in the if statement
len(listname)
determines the length of a list syntax: len()
tuple unpacking
elements of a tuple can be assigned to other variables to be used in normal operations assigned tuple elements can be modified
try and except statements
embeds into a function and the statement under try will be executed If an exception is raised during this execution and that exception matches the keyword in the except statement then the try statement will terminate and the except statement will execute.
another example of the use of list comprehension
messages = [user + " please follow me!" for user in usernames] Takes a string in usernames Assigns that string to a variable called user Adds " please follow me!" to user Appends that concatenation to the new list called messages Repeats steps 1-4 for all of the strings in usernames
collecting multiple returned values
multiple values can be collected through returning by assigning them to variables when calling a function x_squared, y_squared = square_point(1, 3)
returning multiple values
multiple values can be returned by separating them with a comma return low_limit, high_limit
zip syntax
names_and_heights = zip(names, heights)
nested loops
occur when a loop structure exists within another loop structure allows iterating individual situations when needed as a subset of other loops
python int to float conversion
python automatically converts integers into floats when performing division to allow decimal places to exist in the answer
range starting at a number other than 0
range(base number, n + 1 number)
range function that can skip numbers on a pattern
range(base number, n +1, skipping number)
for team in project_teams: for student in team: print(student)
requires indentation and is an example of a nested loop where a loop exists inside of a loop
return keyword
returns a function to the user to be modified or user later can be called in functions
list()
returns a list of the items passed through list(names_and_heights)
selecting the last index of an element or counting backward
selecting last index[start:] (leave the second blank) counting back index[negative:] (leave the second blank)
keyword arguments
specifically and explicitly stating which parameter an argument will be passed into greet_customer(special_item="chips and salsa", grocery_store="Stu's Staples")
starting place of the range function
starts at 0 (based on index)
values that a list can hold
strings numbers other lists emptiness
.append(item)
takes the item in parentheses and adds it to a list can only add one item at a time
zip
takes two or more lists as inputs and returns an object that contain a list of pairs
nth time type function with modulo
the way a modulo function works is that it will spit out the same number pattern from 0 to (divisor - 1). Therefore, it can be used to spit out the same numbers and perform conditional operations based upon the numbers it gives!
while loops
the while loop performs a set of code until some condition is reached
Slice a list
using index[start:end] we can control the range of certain elements to include in a selection lower index starts at the index of the item (to include a nonzero item, use n - 1) upper index needs to be one above our needed selection (n+1)
bool variables in python
values of true and false that can be stored in variables and called for later use can be simply stored as True or False or through a condition that produces the desired true or false state
multiple variables can be added in one line with += syntax
var1 += var2 + var 3
variable declaration and assignment
variableName = Assigned Data variable type is automatically determined by Python
variable changes
variables can be modified in any way but the original variable will not change without reassignment to the variable using =
Boolean Operator: NOT
when applied to any boolean expression it reverses the boolean value. syntax: not So if we have a True statement and apply a not operator we get a False statement.
syntax error
when the syntax rules of the language are violated mistakes that prevent a programming from running or cause it to run improperly to produce a wrong result or no result at all
while loop syntax
while index < len(dog_breeds): print(dog_breeds[index]) index += 1 (to amend the condition that the loop is running on)
index of -1
allows you to select the last index of a list item
parameters
an argument that can be passed into a function to influence the result
infinite loops
loops that never end very dangerous for your programming
exponentiation syntax
(base ** power)
a tuple syntax
(item, item, item) there always needs to be a comma in a tuple, even if there is only one element in the tuple
ZeroDivisionError
Dividing a number by zero (error)
relational operators in python for equal and not equal
Equals: == Not Equals: !=
multiplying strings
Multiplying a string just makes a new string with the old one repeated!
list comprehension
Python rules for creating lists intelligently usernames = [word for word in words if word[0] == '@'] Takes an element in words Assigns that element to a variable called word Checks if word[0] == '@', and if so, it adds word to the new list, usernames. If not, nothing happens. Repeats steps 1-3 for all of the strings in words
Boolean Operators: OR
The boolean operator or combines two expressions into a larger expression that is True if either component is True. syntax: or True : True = True False : False = False False : True = True True : False = True
creating functions
To write a function, you must have a heading and an indented block of code. The heading starts with the keyword def and the name of the function, followed by parentheses, and a colon. The indented block of code performs some sort of operation.
python highlights errors with
a ^ symbol (error highlighting)
function (python)
a collection of several lines of code that can be called without having to repeat multiple lines of code repeatedly
tuple
a data structure in python that allows the user to store multiple pieces of data inside of it Tuples are immutable and cannot be changed or modified after their creation (means no editing)
int()
a function that converts a passed argument into an integer
range(number)
a function that creates a list using a single input and generates numbers starting at 0 to 1 below the provided number range(9) = [0,1,2,3,4,5,6,7,8]
sorted(list)
a function that orders a received list and can be used in assignment because it generates a new list
list.sort() function
a function that orders the received list in ABC or 123 format it does not return anything when called (it just works) so you cannot use it to create new lists through assignment
calling a tuple
a tuple must be called in the exact order as its e
f string
a type of string that is like a template literal from JS that allows calling variables in a string (python 3.6 and later) f"Printed message and called {variable}"
variables
a way of storing data so that it can be called and used as needed within a program variable names cannot have spaces or symbols outside of _ underscore and cannot begin with numbers
calculation syntax
addition: + subtraction: - multiplication: * division: / exponentiation: **
loops
affords capability to: move through each item in a list (for loops) loops that keep going until we tell them to stop (while loops) loops that create new lists (list comprehensions)
selecting list elements with index[]
allows selection of individual items with a zero-index based position syntax: list_name[indexNumber]
break as a part of for loops
allows the program to stop running when the break is hit EX: you perform a search for a particular element in a list and use an if statement to break the program when the intended target is reached
square root calculation in python
exponentiation can be used with fractional exponents to perform root calculations of square and beyond
for loop syntax
for item in list: perform action (indentation is absolutely needed)
using range in a for loop
for variable in range(number): action to perform the number is the number of times the for loop should iterate through the function
print(syntaxHere)
function that tells python to send designated object to console
function calling in python
function_name()
calling a function with a parameter
function_name(parameter)
plus equals
functions to allow the addition of another variable while also allowing assignment variable1 += variable2 adds variable 1 to variable 2 and assigns the new sum to variable1 for storage
modulo operator
gives the remainder of a division operation (the remaining part that is left after all divisible numbers are removed EX: 32 % 3 = 2) gives 0 for wholly divisible numbers the modulo operator is useful when repeated functions are necessary every nth time
use for a tuple
good for data that needs to be stored together and that isn't necessarily similar such as the qualities of a person because they are
remaining relational operators
greater than: > less than: < greater than or equal to: >= less than or equal to: <=
list comprehension example
heights = [161, 164, 156, 144, 158, 170, 163, 163, 157] can_ride_coaster = [height for height in heights if height > 161] print(can_ride_coaster)
if statement syntax:
if 2 == 4 - 2: print("apple") indentation is very important to avoid errors similar to functions in that regard
if...else statement example
if weekday: wake_up("6:30") else: sleep_in()
index error
if you try accessing an index that is too large (or does not exist)
multi-line strings
if you use three quotes at the start and end then the string can go across several lines; the newline characters are included as part of the string
assigning variables with user input
input()
number types
int = a whole number (2) float = a decimal-based number (2.156)
function declaration
is actually called a function definition in python
indentation (whitespace)
is crucial to the execution of functions items not indented properly will not be in the function and will instead be executed on their own or throw errors
scope
limitations applied to variables dependent on the location of their declaration variables declared in functions have functions scope and are not accessible elsewhere (will throw an error when called) variables declared outside functions are accessible inside and outside functions
growing a list with +
lists can be combined and stored together with + new_orders = orders + ['lilac', 'iris']
