Python Tutorial

Meta

This is an exercise in literate programming. Which means the code blocks in this tutorial are executable. A tangled file is also included.

These are my notes from following the Google Developers Python tutorial, W3 Schools Python Tutorials, and Matthes (2016)

Introduction

Python is a “quick and light” language, good for scripting and writing easily.

• Quick turnaround.
• Automation

Python environments

Strings

# Comments being with '#'
string = "Strings are defined with"
string2 = 'double or single quotes'
longString = """Sextuple quotes will define strings
that go over multiple lines
like so"""

Variables

We have seen that we have a number of variables, so far we have created a number of them

  print(string)
# We also have
  print(string2 + " also " + longString)

Variables are named values the syntax of a variable declaration is

variableName = "variable value"

Types

Python has a number of types largely divided into a few larger type buckets

Numerical

Of course numerical types make up part of the different types, there are two basic types of numericals in Python.

integerNum = 5
floatNum = 2.0

These are somewhat compatible on the face of things, but some operations may need some compatibility testing.

Numerical operations

There are of course a number of common numerical operations;

division = integerNum / 2 # Integer arithmetic rules do apply,
# you would expect that this would produce '2.5', however that is a
# float not an integer.
print(division)
# The corollary of division is our modulus operation
modulus = integerNum % 2
print(modulus)
# We can of course utilise float casting to produce a float
floatDivision = float(integerNum) /2
print(floatDivision)

# There are the other operations
multiply = integerNum * 2
print(multiply)

addition = integerNum + 2
print(addition)

subtraction = integerNum - 2
print(subtraction)

# We can also use prefix operations to modify variables eg
addition += 4 # This will add 4 to 'addition' and store it again as addition
print(addition)

Boolean

Boolean variables are values that are either [True | False]

We can use booleans for testing

boolean = True
if 10 > 9:
    print("yes")
# There are other conditionals and we can test multiple using elif and else
a = 33
b = 33
if b > a:
    print("b is greater than a")
elif b < a:
    print("b is less than a")
else a == b:
    print("a and b are equal")
# The logical operators and and or work as expected
if b >= a and b <=a: print ("a and b are equal")
elif b > a or b < a: print ("one is larger than the other")
# We see from the above that we can condense our code

Lists

listA = [ "One string", "Another String", "A third string"]

Lists can be manipulated easily, for instance we can grab the ith element of a list with the syntax list[i]

firstElem = listA[0] # indexation of lists starts at 0
secondElem = listA[1]
# Further we can treat strings themselves as lists
print(firstElem[4])

List operations

There are a number of list operations

# Concatenation
listB = listA + [ string, string2]
listB.extend(listA) # Will do the same as the above
listB.append('hi') # Appending works much the same
# The contents of a list don't have to be the same
listB.append(4)
index = 2
listB.insert(index, "elem") # Inserts "elem" at index
listB.remove(4) # Will remove the first instance of 4
listB.sort() # Sorts the elements of a list
listB.reverse() # Reverses the elements in a list
listB.pop(index) # will remove and return the element at the given index
listB.len() # returns the length of the list

Iteration

The traversal and manipulation of lists is one of the main things that programming is concerned with. The construct for var in list is a simple iterator.

# This code will sum the contents of the list squares
squares = [1, 4, 9, 16]
sum = 0
for num in squares:
    sum += num # As mentioned above the prefix addition looks simpler
    # the alternative looks as follows:
    # sum = sum + num
print(sum) # 30
# There are also functions which produce lists for us to iterate over
for i in range(20):
   print(i)
# We can also iterate otherways for instance with a while loop we can
# iterate over every 3rd item
i = 0
while i < len(listB):
    print(listB[i])
    i += 3

input output

Utilising the variables we’ve set up previously