Introduction to python programming

COMPUTER STUDIES
INTRODUCTION TO PYTHON PROGRAMMING
Python programming is pretty straight forward.
>>> 2 + 3 * 6
20
>>> (2 + 3) * 6
30
>>> 48565878 * 578453
28093077826734
>>> 2 ** 8
256
>>> 23 / 7
3.2857142857142856
>>> 23 // 7
3
>>> 23 % 7
2
>>> 2 + 2
4
>>> (5 - 1) * ((7 + 1) / (3 - 1))
16.0
Order of operation:
B (Brackets) E (Exponent) D (Division) M (Multiplication) A (Addition) S (Subtraction)
Comments:
# this is the first comment
spam = 1 # and this is the second comment
# ... and now a third!
text = "# This is not a comment because it's inside quotes."
Single line comment: # this is a single line comment
Block comments “”” this is a block comments that we must put in a 3 double quote
Like this”””

Basic Arithmetic Operations
Operators:
+: Addition
-: Subtraction
*: Multiplication
/: Division
%: Modulo (remainder). The remainder can be calculated with the % operator
**: Power
//: floor division: if both operands are of type int, floor division is performed and an int is
returned
Variables
Variable = 18
Variable1 = “Hello world!”
Types of variables:
 int: integer 2, 4, 20
 float: the ones with a fractional part or decimal (3.4, 4.9, 3.14,…)
 complex:
 bool: Boolean value (Yes/No; True/False; 0/1)
 str: string this is a strings of characters “I am a string of characters”
Data types: Numbers, Strings, Lists, Tuples, Dictionaries, Lists
Functions
In the context of programming, a function is a named sequence of statements that performs a
desired operation. This operation is specified in a function definition. In Python, the syntax for a
function definition is: print(), input(), round()

Built-in functions
Numbers
Using Python as a Calculator
tax = 12.5 / 100
price = 100.50
bill = price * tax
pay = round(bill, 2)
print(“Your final bil is: “,pay,”$”)
The function round () (like in excel) rounds the result pay into 2 decimal places

Strings
Besides numbers, Python can also manipulate strings, which can be expressed in several ways.
They can be enclosed in single quotes ('...') or double quotes ("...") with the same result [2]. can
be used to escape quotes:
>>> 'spam eggs' # single quotes
'spam eggs'
>>> 'doesn't' # use ' to escape the single quote...
"doesn't"
>>> "doesn't" # ...or use double quotes instead
"doesn't"
>>> '"Yes," he said.'
'"Yes," he said.'
>>> ""Yes," he said."
'"Yes," he said.'
>>> '"Isn't," she said.'
'"Isn't," she said.'
Concatenate strings
Prefix = “Py”
Word = Prefix + “thon”
Lists
Built-in function: len()

Manipulate the element in the list.
Index element in the list
The other way around, if we want to know the index of the element in the list we can use:
This program will return the index of the element “horse” in the list that is 2
Modify, append elements in the list
Let’s modify (replace) “bull” with “parrot”
Bull is replaced by parrot

Extend the list and append elements
If we extend the list the new element is added at the end of the list
How if we move the “bull” at the beginning of the list
Bull is moved at the beginning of the list
Bull is added again in the list

Assignment to slices is also possible, and this can even change the size of the list or clear it
entirely
It is possible to nest lists (create lists containing other lists)

In x= [a, n]
The first element of the list must be a in that case x[0] =”a” and the second element must be
x[1] = n
If we want to show the elements of the list in a it must be written as: x[0][0,1,2]
Instead for the element from n, it is: x[1][0,1,2,3]
Et voilà c’est fait!

The elements of X[0] = [a, b, c]
So from the figure above: X [0] [0] = a; X [0] [1] = b; X [0] [2] = c
The elements of X [1] = [1, 2, 3]
So from the figure above: X [1] [0] = 1; X [1] [1] = 2; X [1] [2] = 3
x [ a , n= ]
First element
X [0]
Second element
X [1]
[0] [1] [2]
[0] [1] [2]

Conditions and Conditional Statements
if, else, elif (Elseif)
<, >, <=, >=, ==, !=
# and, or, not, !=, ==
if 12!=13
print (“YES")
a = 33
t = 22i
if a == 33 and not (t ==22):
print ("TRUE")
else:
print("FALSE")
apples = input("How many apples?")
if apples >= 6:
print ("I have more apples: ")
elif apples < 6:
print ("I have not enough apples: ")
else:
print (" I have nothing: ")
apples = int(input("How many apples?: "))
if apples >= 6:
print ("I have more apples: ",str(apples))
elif apples < 6:
print ("I have not enough apples: ",str(apples))
else:
print (" I have nothing: ",str(apples))
It should say, “I have nothing”
We try to compare string and integer so we need to
convert it into integer using the function int ()

We need to refine the code as follow:
Other way of writing multiple conditions
The use of the operator “and” to combine two
conditions and concatenation

Task1
Write a piece of code to display whether a user inputs 0, 1 or more and display this.
Task2
Write a piece of code to test a mark and achievement by each student.
Mark Grade
91 A*
90 A+
80 A
70 B
60 C
50 D
40 E
30 F
20 Fail

Introduction to python programming

What we have learned so far?
Difference between = and ==
Even though it is a mark the print () function will interpret the value as a string so it is necessary
to convert it using the function str()
All string must be in between “ ” (quotes)
We can concatenate 2 strings using +
While condition
while condition :
indentedBlock
To make things concrete and numerical, suppose the following: The tea starts at 115 degrees
Fahrenheit. You want it at 112 degrees. A chip of ice turns out to lower the temperature one
degree each time. You test the temperature each time, and also print out the temperature before
reducing the temperature. In Python you could write and run the code below, saved in example
program cool.py:
1
2
3
4
5
6
temperature = 115
while temperature > 112: # first while loop code
print(temperature)
temperature = temperature - 1
print('The tea is cool enough.')
I added a final line after the while loop to remind you that execution follows sequentially after a
loop completes.
If you play computer and follow the path of execution, you could generate the following table.
Remember, that each time you reach the end of the indented block after the while heading,
execution returns to the while heading for another test:

Line temperature Comment
1 115
2 115 > 112 is true, do loop
3 prints 115
4 114 115 - 1 is 114, loop back
3 prints 114
4 113 114 - 1 is 113, loop back
3 prints 113
4 112 113 - 1 is 112, loop back
2 112 > 112 is false, skip loop
6 prints that the tea is cool
Each time the end of the indented loop body is reached, execution returns to the while loop
heading for another test. When the test is finally false, execution jumps past the indented body of
the while loop to the next sequential statement.
Test yourself: Following the code. Figure out what is printed. :
i = 4
while i < 9:
print(i)
i = i+2
For Loops
'''The number of repetitions is specified by the user.'''
n = int(input('Enter the number of times to repeat: '))
for i in range(n):
print('This is repetitious!')

Extension
name = input('What is your name? ')
if name.endswith('Gumby'):
print ('Hello, Mr. Gumby')

Introduction to python programming

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