Working with Git and Github

Basic Documentation

Python

Functions and Variables

Spaces matter. No curly braces. No semi-colons.
Create function by

def functionName(num,term):  # no curly braces; yes a colon
   start line with spaces # no semi-colon to indicate end of line
   same number of spaces  # use same number of spaces for same code level

Python lets you call functions with their named parameters named, and not in order.
functionName(term="Spring", num=5)

Set a default value for function with example: def myFunction(n=5):

Fun facts

Statements and Expressions

A statement is a unit of execution; an expression is a unit of evaluation.

In Python:
A statement is a line of code
An expression is any combination of literals, identifiers and operators; anything that returns a value

Data Types

Variables are typed at assignment. Called ‘Duck Typing’ – if it looks like a duck and quacks like a duck it is a duck. Clever. Variable types can be changed – just assign a different type value to it.

variableOne = 4; # It's an integer
print (variableOne + 3) # Returns a 7
variableOne = "four" # Now it's a string
print (variableOne + 3) # Results in error; can't join different types

Use the + to add integers and concatenate strings.
Convert integer to string with str() print (variableOne + str(3))

In Python 3, all types are classes.

The range(x) function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends right before specified number x. range(startNum,stopNum,stepAmt) It stops right before the stop number. Default is range(0,stopNum,1); note that stop number MUST be supplied. 

countByTen = range(10,101,10) # starts at 10, goes up to 100 by tens
for myNum in countByTen:  # instantiates variable myNum as first number in the range
   print(myNum)

Conditionals

If - Elif - Else

if (condition):   # colon
    statements
elif (condition): # colon
    statements
else:             # colon
    statements

Ternary aka Conditional Statement
Basically an If Else all in one line with the condition smack dab in the middle
myString = "X is Bigger!" if (x < y) else "X is NOT Bigger!"

myCondition = someThingThatEvaluates
myTestResult = 'Do This Now' if myCondition else 'Do This Other Thing'
print(myTestResult)

Good god; who bothered to make up the ternary conditional? They should be shot. No, I take that back. It’s kinda cool.

Note: There is no Switch Case in Python.

Loops

Python has only two ways of doing loops: while and for

while(condition): #colon
   statements

for n in range(x,y):
  statements

The For Loop
Other Languages: for (i=0, i<5, i++)
Python: for n in range(x,y,z)
The counter is initialized to x (default 0); the condition is n<y; the step is z.
basically translates to for (i=x, i<y, i+z) and n is set to each iteration.

For Loops also iterate over arrays.

days=["Mon","Tues","Wed","Thurs","Fri","Sat","Sun"]
for d in days:
   print(d)
numbers=[3,4,5,6,7]
for n in numbers:
    print(n) # iterates over entire array

(enumerate(myArray)) will return the index number

days=["Mon","Tues","Wed","Thurs","Fri","Sat","Sun"]
for i,d in enumerate(days):
   print(i, d)  # prints index number and array element

Break: if condition is met, loop terminates and processing falls through to next code block. Continue: if condition is met, skip rest of loop for that iteration and continue from the top

for condition:
   if condition: break
   if condition: continue
   statements

Objects aka Classes

A class is a code template for creating objects. Each object is an instance of its class. When defining a class, the first parameter of any function with the object is called the self parameter. It 1) always refers to the object itself, and 2) is mandatory. It is a reference to the current instance of the class, and is used to access variables that belongs to the class. It is usually named self but you can actually call it whatever you like; it always refers to this instance of the object. Again, it has to be the first parameter of any function in the class.

class personObject:
  def __init__(self, name, age): # init function defines variables that MUST be set at runtime
    self.name = name
    self.age = age

  gender = "" # variables can be instantiated as null

  def myFunc(self):
    print("Hello, my name is " + self.name)

personOne = personObject("James", 14)
print(personOne.age) # prints 14
personOne.myFunc() # prints "Hello, my name is James"
personOne.gender = "male" # set variable value

Misc Libraries

Oh my god so many of them …
Python Standard Library
Import Date and Time: from datetime import [date, time, datetime, timedelta]

now = datetime.now() # built in method
print("It is now " , now)
print("Later on, it will be: ", now + timedelta(days=60, hours=10, minutes=7)) # built in method

Data Structures

Recursion

When a program calls itself. There must be a breaking condition in order to avoid infinite loops. A call stack (implemented with Stack data structure, above) keeps track of the arguments.

Sorting

These are serious mathematical puzzle solving solutions.

Searching

Strings in Python

Define multi-line strings with three quotes and it will print that way.

 myString = '''
   a whole bunch of lines of text
   more and more text
 '''

Reference characters in strings by their index value. Example: myMessage = 'Python for Beginners'
myMessage[0] will return ‘P’; myMessage[7] returns ‘f’; AND you can count backwards: myMessage[-1] returns the last character in the string.
myMessage[0:3] returns a range. As in all Python ranges, the range stops right BEFORE the specified index; that is, the character at the specified index number is not included in the return set. Ranges: default start = 0; default end = 0. So [:] is essentially “start to end”

Formatted Strings

Formatted Strings make it easier to visualize the output of a dynamically generated string.
A formatted string is prefixed with an ‘f’.

message = f'{firstName} {lastName} is {status}' Note the awesomeness of not having to concatenate it all.

String Methods

len(myString): length (This function is actually general purpose; not a string method)

myString.AllKindsOfStuff() <br />
myString.find('n') # Returns an index number; if not found, returns -1
myString.replace('C','K') # Changes out first for second

‘IN’ operator: returns true or false.
'James' in myString

Arithmetic Operations

Number types: Integers and Floats
Operators: + addition; - subtraction; / division; // division return integer; % division return remainder; ** power of
Augmented Assignment Operators: +=; -=

Python Code Template

def main():
  all the code here

if __name__ == '__main__': main()

This little conditional statement is a common way of writing python. It forces the interpreter to read the entire script before it executes any of the code; allowing a more procedural style of programming.

Working with Dictionaries

Dictionaries: ordered, indexed, changable, key/value pairs. Braces.
print(dictionaryName) will print contents 

myCar =	{"brand": "Ford", "model": "Mustang", "year": 1964} <br />
print(myCar)  # prints entire thing

Get value of key:
x = myCar['brand'] returns ‘Ford’
x = myCar.get['brand'] returns ‘Ford’
Change value of a key:
myCar['year'] = '1960'

Check if key is present:

if "model" in myCar:
  print("Model is here")

How many Key/Value pairs?

x = len(myCar)
print(x)

Add Key/Value pair by adding a Key/Value pair:
myCar["color"] = "red"

Remove with pop() method or del keyword:
myCar.pop("model") or del myCar["model"]

myCar.clear() cleans it out newCar = myCar.copy() makes a copy of the dictionary newCar = dict(myCar) also makes a copy of the dictionary

Use For Loop to 1) Print Key Names

for car in myCar:
   print(car)

2) Print Values

for x in myCar:
   print(myCar[x])

for x in myCar.values():
     print(x)

3) Print Keys and Values

for x, y in myCar.items():
  print(x, y)

Nested Dictionaries

child1 = {"name": "Emil", "year": 2004}
child2 = {"name": "Tobias", "year": 2007}
child3 = {"name": "Linus", "year": 2011}

myFamily = {
  "first": child1,
  "second": child2,
  "third": child3
}

print(myFamily) returns entire dictionary

for myChild in myFamily:
   print(myFamily[myChild])

returns the child dictionaries

print(myFamily["first"])
print(myFamily["second"]["name"])

Iterate through a nested dictionary:

for childKey, childInfo in myFamily.items():
    print("\nChild the", childKey)
    for key in childInfo:
        print(key + ':', childInfo[key])
    for kk, vv in childInfo.items():
        print(kk + ':', vv)

back