Understanding Python's Range Function

Range Function

• The range() function creates a sequence of numbers.
• It starts from 0 by default.
• Range function is typically used for generating a series of numbers for iterations.

Range Syntax

• The complete syntax for the range() function is range(start, stop, step).

Range Default Step

• If the step is not specified when using the range() function, Python defaults to a step of 1.

Code Example: Looping With Range

• for x in range(10): print(x, end=" ") prints numbers from 0 to 9, all on the same line.

Code Example: Range With Start, Stop, Step

• for x in range(1, 9, 2): print(x) prints the numbers 1, 3, 5, and 7, each on a new line.

Code Example: Summation Using Range

S = 0
for x in range(1, 9):
    S = S + 1
print(S)

• The code outputs the sum of incrementing S from 1 to 8

For Loop Syntax

• The correct syntax for a for loop is for <variable> in range(start, stop, step): <block of code>.

Negative Stepping With Range

• range(101, 2, -1) creates a sequence of numbers from 101 down to 3.

Errors With Range Stepping

• The code for x in range(9, 2, 0): print(x) results in an error because the step cannot be zero.

While Loop Syntax

• The correct syntax for a while loop is while <condition>: <block of code>.
• The block of code in a while loop executes as long as the condition is true.

Basic Programming Constructs

• The basic programming constructs of most programming languages are: sequential execution, loops, and conditional branching.

Exiting Loops

• The break statement can be used to immediately stop and exit a while or for loop.

Code Example: While Loop Increment

i = 1
while i < 20:
    i = i + 3

• The final value of i is calculated by repeatedly adding 3 to i

Code Example: While Loop Summation

i = 1
s = 0
while s < 20:
    s = s + i
    i = i + 2

• The result depends on the accumulated sum s not exceeding 20

Code Example: Conditional Increment in Loop

i = 1
d = 0
while i < 20:
    if i % 3 == 0:
        d = d + 1
    i = i + 2

• d gets incremented only when i is a multiple of 3

Code Example: Even Number Summation in Loop

i = 1
s = 0
while i < 20:
    if i % 2 == 0:
        s = s + i
    i = i + 2

• The code calculates the sum of even numbers

Loop Execution Count

i = 1
s = 0
while i < 20:
    s = s + i
    i = i + 5

• The number of times the block of code is executed depends on how quickly i increments and reaches 20

While Loop Characteristics

• While loops continue as long as a condition is true and are suitable when the number of iterations is unknown.

Conditional Statement Errors

• The code for x in range(5): print(y) may produce an error if y is not defined.

List Data Types

• Valid ways to initialize a list are Ds = [] and Ds = [1.5, 2, 3, "9", "10"].

List Data Type Properties

• List data types have elements that can be of different types.
• Indexes in lists begin at 0.
• Lists allow modification of its elements.

List Length

a = [4, 3, -2, -3, 5, 6, 4]
len(a)

• The len() function returns the number of elements in the list.

List Element Insertion

• The command A.append(100) adds the value 100 to the end of the list.
• The command A.insert(3, 6) inserts the number 6 at the index 3 of the list A.

List Concatenation

List1 = [1, 2, 3, 4]
List2 = [5, 6, 7, 8]
print(len(List1 + List2))

• The code returns the combined length of List1 and List2.

Removing List Elements

• del A[len(A) - 1] removes the last element of list A.

Adding Element To Beginning of List

• list = [x] + list adds element x to the beginning of the list.

Printing List Items

for i in range(len(B)):
    print(B[i], end=" ")

• The code prints each element of list B on the same line, separated by a space.

Deleting Multiple List Elements

• del a[0:2] removes the elements at positions 0 and 1 from list a.
• A.clear() removes all data from list A

Printing List Element Values

A = [8, 7, 4, 11, 35]
for k in A:
    print(k, end=' ')

• In the loop, k takes on the values of each element in A

Using input() Function

• n = int(input()) reads an integer from the user.
• n = input() reads a string from the user.
• print(n * "*") prints the "*" character n times.

Removing List Elements by Value

A = [4, 7, 8, 6, 7]
A.remove(8)

• The code removes the first occurrence of the value 8 from the list

Loop Output Sequencing

n = int(input())
for i in range(n - 1, 0, -1):
    print(i, end=" ")

• The code prints a sequence of numbers in reverse order

List Transformations Based on Condition

a = list(map(int, input().split()))
b = []
c = []
for i in a:
    if i % 2 == 0:
        b.append(i)
    else:
        c.append(i)
d = b + c
for i in d:
    print(i, end=" ")

• Code moves even numbers to the beginning and odd numbers to the end

Conditional Printing in Loops

n = int(input())
i = 1
while i <= n:
    if i % 10 != 0:
        print(i, end=" ")
    if i % 10 == 0:
        print(i)
    i += 1

• The numbers not divisible by 10 are printed on same line; numbers divisible by 10 are printed on their own line.

String Definition

• Strings in Python are a sequence of characters.

Empty String

• An empty string is a string with no characters.

Strings vs Lists

• Strings cannot be changed after they are created, but lists can be modified.

String Delimiters

• Strings can be represented using single quotes, double quotes, or triple quotes.

String Length

• The length of a string is obtained using the len() function.

String Iteration

• Characters in a string can be accessed iterating using a for loop.

String Membership

• The in operator checks if a substring is part of another string.

Substring Extraction

s = "abcdefghi"
k = len(s) // 2
s1 = ""
for i in range(k):
    s1 = s1 + s[i]

• Code finds the substring from the start to the middle of the string

String Concatenation

a = "hello"
b = "world"
c = a + " " + b
print(c)

• The code concatenates two strings with a space in between

Combining List Into Word

• Use the join() command to join a list into a word

String Splitting

• Use the split() command to split word into list

String Pattern Matching

• s.find(" ") finds the index of the first space character in the string