Introduction to Python Programming - Part - II

Instructor: Dr. Sanasam Ranbir Singh

This tutorial is prepared by Mr. Vijay Purohit, Dept. of CSE, IIT Guwahati

1. FUNCTIONS

---

It is a named unit of a group of program statment. It can be invoked from other parts of the program as and when require.
It is basically a subprogram that acts on a data and can returns data.

> Relatable f:X→Y y=f(x)?

User Defined Functions: These are defined by the user at the time of writing a program as per requirements of the program.
Built-in (or Library) funtions: There are the part of library, as we have seen in last class print(), int(), float(), input()

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#Some Built-In Funtions: input(), float(), type(), print() 
price = float(input('Enter the price: ')) 
print(type(price)) 
print("Current Price mentioned is {}".format(price)) 
print(f"The cost is {price} Rupees.")

2. Function Definition and Call

```

def function_name(parameter: data_type) -> return_type:

""" docstring """

body of the function

return expression

```

Take Care of Indentation
To execute a funtion, you must call it
When a function is called, the interpreter jumps to that function and executed the statments in its block. Then, when the end of the block is reached, the interpreter jumps back to the part of the prgram that called the function, and the program resmes execution at that point.

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#We defined a function named message. (notice the colon)
def message(): 
  print("Welcome to LAB-02.")

#call the message function
message()

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#FLOW OF PROGRAM
print("1. statment BEFORE the function definiton with parameters")
#Function Definition with PARAMETERS 
def message(name): 
  print("Welcome to LAB-02 of "+name)

print("2. statment AFTER the function definiton")

#call the message function with ARGUMENTS
message("Python class")

print("3. statment AFTER the function CALL with Arguments")

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#for people with prior experience in langugages like c/c++ or java 
# def add2nums(num1, num2) -> int:                  #with syntax 1
def add2nums(num1: int, num2: int) -> int:         #with syntax 2 data type -> return type
  """ This functions add two numbers"""           #doc string   
  num3 = num1+num2
  return num3               # return statment

num1, num2 = 5, 10
ans = add2nums(num1, num2) #function call
print(f"The addition of {num1} and {num2} is: {ans}.") 

# about docstring\
#Syntax: print(function_name.__doc__)
#print(add2nums.__doc__)

3. Types of Arguments

Default Arguments:

Once we have a default argument, all the arguments to its right must also have default values.

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#def fun_arg(x=1, y, z=3):
def fun_arg(x, y, z=3):
  print("x: ", x)
  print("y: ", y)
  print("z: ", z)  

#fun_arg(1, 2)
fun_arg(1, 2, 4)

Keyword Arguments:

Using this way, the order(position) of the arguments can be changed.

Keyword arguments must follow positional arguments.

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def courseName(firstName, lastName):
  print(firstName, lastName)

courseName(firstName="Python-", lastName="Programming") #keywords arguments
courseName(lastName="Programming ", firstName="Python-") #out of order
courseName("Python-", lastName="Programming 2") #1 positional, 1 keyword

Variable Length Arguments:

variable number of arguments to a function

*args (non-keyword arguments)
**kwargs (keyword arguments)

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def varArgs(*argv):
  for item in argv:
    print(item, end="-")

varArgs('1', '2', '3', '4', '5', '6', '7', '8', '9')
print()
def varArgs(**keyArgv):
  for key,value in keyArgv.items():
    print(key,"-", value, end="|")

varArgs(one='1', two='2', three='3', four='4', five='5', six='6', seven='7', eight='8', nine='9')

4. Return Statement

```

syntax: return [expression_list]

```

It can consist of a variable, an expression, or a constant which is returned to the end of the function execution

5. Recursive Function

A function calling itself.

recursive approach

In [ ]:

def factorial(x):
  """This is a recursive function to find the factorial of an integer""" 
  print(x, end='*')
  if x == 1:
    return 1
  else:
    return (x * factorial(x-1))
num = 6
print("\nThe factorial of", num, "is", factorial(num))

More about it here

6.Variables Type

Global Variables

A variable declared outside of the function or in global scope.

In [ ]:

x = "global" 
def foo():
  print("inside foo func:", x) 
foo()
print("main:", x)

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x = "global" 
def foo():
  #global x
  x = x*2
  print("inside foo func:", x) 
foo()
print("main:", x)

Local Variables

A variable declared inside the function's body or in the local scope.

In [ ]:


def foo():
  y = "local" 
  print("inside foo func:", y) 
foo()
print("main:", y) #error

7. Modules

A file that contains Python code.

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import math
#import math as m
def area(radius):
  #return m.pi * radius**2
  return math.pi * radius**2
area(3.4)

LISTS AND TUPLES

A sequence is an object that contains multiple items of data.

Two of the Fundamental Sequence Types: lists and tuples.

Both can hold various types of data.
Difference: a list is mutable, which means that a program can change its contents.

Surrounded by square brackets [ ]

But a tuple is immutable, which means that once it is created, its contents cannot be changed.

Surrounded by parenthesis ( )

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# List of even integers
even = [2, 4, 6, 8, 10]
print("even: ",even)
print("even size: ",len(even)) #length of list

# List of names
names = ["python", "c++", "rust"]
print("names: ",names)

# List with mixed data types
mixture = [1, "Hi", 3.4]
print("mixture: ",mixture)
print("mixture size: ",len(mixture)) #size of list

# Nested List
nested = ["top", [8, 4, 6], ['a']]
print("nested: ",nested)
print("nested size: ",len(nested)) #size of list

# list() function to convert type of objects to list
numbers = list(range(1, 10, 2))
print("numbers: ",numbers)

1. Accessing Elements

Refer to the index number. Use the index operator [ ] to access an item in a list.
The index must be an integer.
Nested lists are accessed using nested indexing.

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# Nested List
nested = ["top", [8, 4, 6], ['a']]
print("nested[0]: ",nested[0]) # 1st element
print("nested[1]: ",nested[1])
print("nested[1][0]: ",nested[1][0]) # multi-dimension
print("nested[2]: ",nested[2])

Negative Indexing
represent positions from the end of the array. (means beginning from the end).

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# Nested List
nested = ["top", [8, 4, 6], ['a']]
print("nested[-1]: ",nested[-1]) # last element
print("nested[-3]: ",nested[1]) #last third item
print("nested[1][-1]: ",nested[1][-1]) # multi-dimension

2. List Functions

2a. Append Method:

one element/tuple/existinglist at a time can be added to the list by using append() function

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even = [2]
even.append(8)  #append elements
even.append(12)
print("even: ",even) 
 
names = ["python", ]
names.append(("c++", "java")) #append tuples
print("names: ",names)

nested = ["top", 'a']
nested.append(even)
print("nested: ",nested)

2b. Insert Method:

To insert elements at the desired position

```

list.insert(position, value)

```

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even = [2, 8, 12]
even.insert(1, 4)  
print("even: ",even) 
even.insert(3, 10)  
print("even: ",even)

2c. Remove Method

remove the first occurrence of the specified item

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even = [2, 4, 8, 12, 4]
even.remove(4)  
print("even: ",even) 
even.remove(4)  
print("even: ",even)

2d. Pop Method

by default remove only the last element of the list. To remove an element from specific position of the list, the index of the element is passed as an argument.

Del Statment

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even = [2, 4, 8, 12, 4]
item = even.pop()  
print("item: ",item) 
print("pop even: ",even) 
even.pop(1)  
print("pop even: ",even) 

even = [2, 4, 8, 12, 4]
del even[2] 
print("del even: ",even)

2e. Sort Method

sort elements in ascending order

2f. Reverse Method

reverse the list

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even = [2, 4, 8, 12]
even.reverse()   
print("even: ",even) 

even = [14, 12, 8, 4, 2] 
even.sort()
print("even: ",even)

2g. min and max function

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even = [12, 4, 16, 8, 10, 2, 22]
print("min in even: ",min(even))
print("max in even: ",max(even))

3. Some Operations on Lists

3a. Contcatenating Lists

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list1 = [1, 2, 3, 4]
list2 = [8, 7, 6, 5]
list3 = list1 + list2 
print(list3)

3b. Copying Lists

both lists will reference the same list in the memory

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list1 = [1, 2, 3, 4]
list2 = [8, 7, 6, 5]
list2 = list1 #both lists will reference the same list in the memory
list1[0] = 0
print(list1)
print(list2)

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list1 = [1, 2, 3, 4]
list2 = []+list1 #different copy
list1[0] = 0
print(list1)
print(list2)

3c. Finding items in Lists Using in Operator

```

syntax: item in list

```

returns true if item is found in the list, or false otherwise

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list1 = [1, 2, 8, 7, 6, 5, 3, 4] 
if 3 in list1:
  print("found")
else:
  print("not found")

**3d. * operator (repetition operator)**

```

syntax: list * n

left side: list

right side: integer

```

It makes multiple copies of a list and joins them all together

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numbers = [1,2,3]*3
print(numbers)

4. List Slicing

slices: subsections of a sequence

```

list_name[start: end]

```

start is the index of the first element.
end is the index marking the end of the slice
elements include from start up (but not including) end

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days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday']
mid_days = days[2:5]
print("days: ",days) 
print("mid_days: ",mid_days) 

first2_days = days[:2] # elements from begining till given index
print("first2_days: ",first2_days) 

last_days = days[5:] # elements from specific index till the end
print("last_days: ",last_days) 

all_days = days[:] # 
print("all_days: ",all_days) 

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
even = numbers[1:8:2] # step value of 2 
print("even: ",even) 

n = numbers[-5:]  #negative indexing
print("n: ",n)

all = numbers[::-1]  #in reverse order
print("all: ",all)

5. Two Dimensional Lists

nested list or two-dimensional lists

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matrix = [[4, 17, 34, 24], [46, 21, 54, 10], [54, 92, 20, 100]]
for r in range(3):
  for c in range(4):
    print(matrix[r][c], end=" ")
  print()

6. TUPLES

A tuple is a sequence, like a list.
immutable, once created cannot be changed.
enclosed in parentheses ( )
support all the same operations as lists, except those that change the contents.

supports
len, min, max, in, +, *
slicing expressions, index, subscript indexing
does not supports
append, remove, insert, reverse, and sort

adv:
faster performance
safe

```

tuple_name = tuple(str_list)

```

STRINGS

strings are immuatable

1. Accessing Individual Characters in a String

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name ="Python Programming"
for ch in name:
  print(ch, end="-")
print()
ch = name[5]
print("ch: ", ch)


print("len of name: ", len(name)) #length function

2. String Concatenation

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message = "Hello" + ' ' + "world"
print(message)

3. String Slicing

slices: substrings of a string

```

string[start: end]

```

start is the index of the first character.
end is the index marking the end of the slice
return a string containing a copy of the characters from start up to (but not including) end.

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full_name = "Amar Akbar Anthony"
middle_name = full_name[5:10]
print("middle_name[5:10]: ",middle_name)

first_name = full_name[:4]
print("first_name[5:10]: ",first_name)

last_name = full_name[11:]
print("last_name[11:]: ",last_name)

last_name_neg = full_name[-6:]
print("last_name_neg[-6:]: ",last_name_neg)

name = full_name[:]
print("name[:]: ",name)

letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
print("letters ",letters[0:26:2]) #step value of 2

4. TESTING, SEARCHING AND MANUPULATING STRINGS

general format for string method call

```

syntax: stringvar.method(arguments)

```

4a. Testing Strings with `in` and `not in`

```

syntax: string1 in string2

```

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text = 'Four and seven years ago'
if 'seven' in text:
 print('The string "seven" was found.')
else:
 print('The string "seven" was not found.')

names = 'Amar akbar anthony ram shyam vijay'
if 'ravan' not in names:
 print('ravan was not found.')
else:
 print('ravan was found.')

4b. String Testing Methods

more ref: here

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string1 = '1200'
#string1 = '1200abc'
if string1.isdigit():
 print(string1, 'contains only digits.')
else:
 print(string1, 'contains characters other than digits.')

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# This program demonstrates several string testing methods.
def main():
  user_string = input('Enter a string: ')  
  # Test the string.
  if user_string.isalnum():
    print('The string is alphanumeric.')
  if user_string.isdigit():
    print('The string contains only digits.')
  if user_string.isalpha():
    print('The string contains only alphabetic characters.')
  if user_string.isspace():
    print('The string contains only whitespace characters.')
  if user_string.islower():
    print('The letters in the string are all lowercase.')
  if user_string.isupper():
    print('The letters in the string are all uppercase.')

#Call the string.
main()

4c. String Modification Methods

returns modified versions of strings

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# This program demonstrates several string testing methods.
user_string = "Wx Yz Ab cde"
print("lower: ", user_string.lower())
print("lower: ", user_string.upper())

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#endswith(substring): returns true if the string ends with substring
filename = "data.txt"
if filename.endswith('.txt'):
 print('That is the name of a text file.')
else:
 print('Unknown file type.')

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#find(substring): returns the lowest index in the string where substring is found. else returns −1.
string = 'Four and seven years ago'
position = string.find('seven')
if position != -1:
  print('The word "seven" was found at index', position)
else:
  print('The word "seven" was not found.')

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#replace(old, new)  returns a copy of the string with all instances of old replaced by new.
string = 'Four and seven years ago'
new_string = string.replace('years', 'days')
print(new_string)

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#repetition operator *
print('Hello' * 5)

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# split() : returns a list containing the words in the string.
my_string = 'One two three four' 
# Split the string.
word_list = my_string.split()
print(word_list[1])
print(word_list)

date_string = '11/26/2018'
date_list = date_string.split('/')

In [ ]:

Python-02.ipynb

Introduction to Python Programming - Part - II

1. FUNCTIONS

2. Function Definition and Call

body of the function

3. Types of Arguments

4. Return Statement

5. Recursive Function

6.Variables Type

7. Modules

LISTS AND TUPLES

1. Accessing Elements

2. List Functions

3. Some Operations on Lists

4. List Slicing

5. Two Dimensional Lists

6. TUPLES

STRINGS

1. Accessing Individual Characters in a String

2. String Concatenation

3. String Slicing

4. TESTING, SEARCHING AND MANUPULATING STRINGS

4a. Testing Strings with in and not in

4b. String Testing Methods

4a. Testing Strings with `in` and `not in`