MNNIT CC 2021-22 Classes

Python Class - I

Python Class - I recording: Here

May 06, 2021

python

What is Python?

Strings and Printing in Python

print("Hello World!")
print("I like typing this.")
print("_-"*40)

string0 ='Welcome to first class of python'
string1 ="Welcome to first class of python"
string2 = """Welcome to first
class
of
python"""

print(string0)
print("_-"*40)
print(string1)
print("_-"*40)
print(string2)

Hello World!
I like typing this.
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
Welcome to first class of python
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
Welcome to first class of python
_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-
Welcome to first
class
of
python

Indexing and slicing

In python, indexing starts from 0.

name ="asdfghj"
print(name[0])        # Char at index 0
print(name[-1])
print(name[0:4])      # Substring from index 0 to 3
print(name[2:])       # Substring from index 2 to end of string
print(name[:3])       # Substring from start to index 2 
print(name[:])        # Substring from start to end
print(name[2:5:2])    # Characters from index 2 to 4 in steps of 2
print(name[::-1])     # Complete string taking a step of -1

a
j
asdf
dfghj
asd
asdfghj
dg
jhgfdsa

Built-in functions

len() function is an inbuilt function in Python programming language that returns the length of the string.

find( ) function returns the index value of the given data that is to found in the string. If it is not found it returns -1. One can also input find( ) function between which index values it has to search.

index( ) works the same way as find( ) function the only difference is find returns ‘-1’ when the input element is not found in the string but index( ) function throws a ValueError

print(len(name))

print(name.find("df"))      # First index where "dy" is found
print(name.find("ty"))      # Returns -1 if not found
print(name.find("df",2,5))  # finds string from index 2 to 4
print(name.find("df",4,6))

print(name.index('df'))
print(name.index('ty'))     # error

7
2
-1
2
-1
2



---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-21-e6c75499e80c> in <module>
      7 
      8 print(name.index('df'))
----> 9 print(name.index('ty'))     #error


ValueError: substring not found

capitalize( ) is used to capitalize the first element in the string.

lower( ) converts any capital letter to small letter.

upper( ) converts any small letter to capital letter.

endswith( ) function is used to check if the given string ends with the particular character(s) which is given as input.

count( ) function counts the number of char in the given string. The start and the stop index can also be specified or left blank.

print(name.capitalize())
print(name.lower())
print(name.upper())
print(name)

print(name.endswith('j'))
print(name.endswith('a'))

print(name.count('a',0,7)) # Start and end index mentioned
print(name.count('a'))
print(name.count('b'))

Asdfghj
asdfghj
ASDFGHJ
asdfghj
True
False
1
1
0

end and sep parameters in print()

end -

sep -

print("Hello Again!", end="")
print("I like typing this.")

print("\n", "_-"*40, '\n')

# Printing multiple strings using single print statement
print("CC", "classes")
print("CC", "classes", sep = ' & ')

print("\n", "_-"*40, '\n')

print("End","and","sep","together","in", sep = " _ ", end=" _print")

Hello Again!I like typing this.

 _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- 

CC classes
CC & classes

 _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- 

End _ and _ sep _ together _ in _print

Variables and Datatypes

# Integer - int
a = 10
print(a, type(a))

# String - str
b = "Computer Coding Club"
print(b, type(b))

# Float - float
num = 3.244
print(num, type(num))

# Boolean - bool
flag = False
print(flag, type(flag))

10 <class 'int'>
Computer Coding Club <class 'str'>
3.244 <class 'float'>
False <class 'bool'>

Python Arithmetic Operators

print("Addition: ", 2 + 3, ",", 3.4 + 5.677)

print("Substraction: ", 2 - 3, ",", 10 - 2.43)

print("Multiplication", 3 * 4, ",", 4.3 * 5.1)

print("Division: ", 12 / 5, ",", 10 / 2)

print("Modulus: ", 20 % 10, ",", 23 % 6)

print("Exponentiation: ", 5**3, ",", 2**4)

print("Floor Division: ", 12 // 5, ",", 10 // 2)

Addition:  5 , 9.077
Substraction:  -1 , 7.57
Multiplication 12 , 21.929999999999996
Division:  2.4 , 5.0
Modulus:  0 , 5
Exponentiation:  125 , 16
Floor Division:  2 , 5

Comments in Python

# Comments in python
# Comment  -> 
# This is a comment

"""
multiple comment
print("Python" + "Class")
"""

Data Structures in Python

We will talk about 4 basic data structures.

1. List -

# List of strings
prog_langs = ["C++", "C", "Python", "JS"]
hetero_list = ["Foo", 23, True, 3.46, "Is this possible?"]

# Printing List
print(prog_langs)
print(hetero_list)

# Accessing single item from list (indexing)

# Positive Indexing
lang1 = prog_langs[0] 
lang2 = prog_langs[2]
print("Lang1: ", lang1)
print("Lang2: ", lang2)

# Negative Indexing
lang3 = prog_langs[-1]
lang4 = prog_langs[-2]
print("Lang3: ", lang3)
print("Lang4: ", lang4)

# Lists are mutable
prog_langs[0] = "Java"
print(prog_langs)

# Adding an element to existing list
prog_langs.append("C#")
print("After appending: ", prog_langs)

# Length of list
print("Length: ", len(prog_langs))

# Deleting an element from list
del prog_langs[1] # Deleting 'C'
print("After deleting: ", prog_langs)

['C++', 'C', 'Python', 'JS']
['Foo', 23, True, 3.46, 'Is this possible?']
Lang1:  C++
Lang2:  Python
Lang3:  JS
Lang4:  Python
['Java', 'C', 'Python', 'JS']
After appending:  ['Java', 'C', 'Python', 'JS', 'C#']
Length:  5
After deleting:  ['Java', 'Python', 'JS', 'C#']


2. Tuple -

# Tuple of Strings
colors = ("Red", "Blue", "Green")
print(colors)
# Heterogenous tuple
hetero_tuple = ("Possible?", 2.3, 4, True, [1, "Again"], (2, 5.67, "CC Classes"))
print(hetero_tuple)

print("Positive Indexing: ", hetero_tuple[2])
print("Negative Indexing: ", hetero_tuple[-1])

('Red', 'Blue', 'Green')
('Possible?', 2.3, 4, True, [1, 'Again'], (2, 5.67, 'CC Classes'))
Positive Indexing:  4
Negative Indexing:  (2, 5.67, 'CC Classes')

# Tuple is Immuatable - trying to reassign
colors[0] = "Purple" # This will give error

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-23-036b598c976c> in <module>
      1 # Tuple is Immuatable
----> 2 colors[0] = "Purple" # This will give error


TypeError: 'tuple' object does not support item assignment

# Tuple is Immutable - trying to delete
del colors[2] # Again error

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

<ipython-input-24-2fe37e6741af> in <module>
      1 # Tuple is Immutable - trying to delete
----> 2 del colors[2] # Again error


TypeError: 'tuple' object doesn't support item deletion

3. Set -

myset = {3,2,1}
fruits = {"apple", "banana", "cherry"}
print(myset)
print(fruits)

myset.add(4)
myset.add(8)
myset.add(4)
print("After adding: ", myset)

myset.pop()
print("After popping: ", myset)

myset.remove(3)
print("After removing 3: ", myset)

myset.discard(2)
print("After discarding 2: ", myset)

{1, 2, 3}
{'apple', 'banana', 'cherry'}
After adding:  {1, 2, 3, 4, 8}
After popping:  {2, 3, 4, 8}
After removing 3:  {2, 4, 8}
After discarding 2:  {4, 8}

Difference in remove() and discard()

remove() raises an error if element to be removed is not present in the set whereas discard() does not raise error even if element to be discarded is not present.

4. dictionary -

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

# Accessing value using key
print("Brand: ", thisdict["brand"])
print("Model: ", thisdict.get("model"))

# Adding a key value pair to dictionary
thisdict["electric"] = False
thisdict.update({"color": "green"})
print("After updating: ", thisdict)

# Printing all keys of dictionary
print("Keys: ", thisdict.keys())

# Deleting a key-value pair
thisdict.pop("color")
print("After popping: ", thisdict)

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}
Brand:  Ford
Model:  Mustang
After updating:  {'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'electric': False, 'color': 'green'}
Keys:  dict_keys(['brand', 'model', 'year', 'electric', 'color'])
After popping:  {'brand': 'Ford', 'model': 'Mustang', 'year': 1964, 'electric': False}

Control Statements - if, elif, else

To write the statements inside if or elif or else, we first have to give indentation. Press tab for that.

# If-Else conditions Syntax

# if condition :
#      statements
# elif condition:
#      statements
# else:
#      statements

age = 13
if age < 18:
    print("You cannot vote!")

# Use of "is" operator
#name = "Foo"
name = "Bar"
if name is "Foo":
    print("Hey there Foo")
elif name == "Bar":
    print("What's up Bar!")
else:
    print("Please sign up for the site!")
    
# Use of "in" operator
students = ["Alice", "Bob", "Foo", "Bar"]
stu_name = "Bob"
if stu_name in students:
    print("Hello", stu_name, "You are enrolled")
else:
    print("You are not enrolled!")
    
# Use of "and" operator
user_name = "abc"
password = "123"
if user_name is "abc" and password = "123":
    print("Access granted")
else:
    print("Access denied")

# Use of "or" operator
age = 30
if age <10 or age >25:
    print ("Not golden years")
else:
    print("Golden years")

You cannot vote!
What's up Bar!
Hello Bob You are enrolled
Access granted
Not golden years

Loops in Python - for, while

# For loop
# from 0 to 9
for x in range(10):
    print(x, end=",")

print("")

# from 5 to 11
for x in range(5, 12):
    print(x, end=",")

print("")

# from 10 to 40 (not included), increment value 5
for x in range(10, 40, 5):
    print(x, end=",")

print("")

# While loop
i = 5
while i < 10:
    print(i, end=",")
    i += 1

print("")

# Adding elements to an empty list
mylist = []
for x in range(10, 20, 3):
    mylist.append(x)

print("My List: ", mylist)

0,1,2,3,4,5,6,7,8,9,
5,6,7,8,9,10,11,
10,15,20,25,30,35,
5,6,7,8,9,
My List:  [10, 13, 16, 19]

# Iterating over list in Python
colors = ["Red", "Green", "Blue", "White", "Black"]
for color in colors:
    print(color)

print("")
# Iterating over a dictionary
thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

for key in thisdict.keys():
    print("Key:", key, "| Value:", thisdict[key])

print("")

for key, value in thisdict.items():
    print("Key:", key, "| Value:", value)

Red
Green
Blue
White
Black

Key: brand | Value: Ford
Key: model | Value: Mustang
Key: year | Value: 1964

Key: brand | Value: Ford
Key: model | Value: Mustang
Key: year | Value: 1964

Functions

Basic Syntax

def function_name(parameters):

"""docstring"""        (optional) 
  statement(s)
  return statement (optional)

Syntax of return statement

return [expression_list]

# Funciton without parameters

# Defining function
def func():
    print('Hello')

# Calling function    
func()

Hello

# Function with parameters
def purchase(egg_count):
  print(egg_count)

purchase(10)

10

# Funcgtion with default parameters
def purchase(egg_count=10):
  print(egg_count)

purchase()
purchase(20)

def greet(name, msg = "Good morning!"):
    print(name,msg)
    
greet("Alice")
greet("Foo Bar")
greet("Bob", "Good Afternoon!")

10
20
Alice Good morning!
Foo Bar Good morning!
Bob Good Afternoon!

# SyntaxError: non-default argument follows default argument
def greet(msg = "Good morning!", name):
    print(name,msg)
    
greet("Alice")

  File "<ipython-input-27-0dc9fc45140b>", line 2
    def greet(msg = "Good morning!", name):
             ^
SyntaxError: non-default argument follows default argument

# Function with return statement
def purchase(egg_count=10):
  return 10 * egg_count

answer = purchase()
print(answer)

answer = purchase(15)
print(answer)

Note: Rest of the content have been moved to next class here.

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