Python Revision P1 (Data Types, Conditions, String Method, Calculation, Input Output, Operators)

Python Summary Cheat Sheet - 1

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Data Types in Python

In programming languages, every value or data has an associated type to it known as data type. Some commonly used data types.

String: A String is a stream of characters enclosed within quotes.

"Hello World!"
1234

Integer: All the numbers (positive, negative and zero) without any fractional part come under Integers.

...-3, -2, -1, 0, 1, 2, 3,...

Float: Any number with a decimal point.

24.3, 345.210, -321.86

Boolean: In a general sense, anything that can take one of two possible values is considered a Boolean. As per the Python Syntax, True and False are considered as Boolean values.

True, False

Conditional Statements

Conditional Statement: Conditional Statement allows you to execute a block of code only when a specific condition is True.

if True:
    print("If Block")  
    print("Inside If") 

# Output is:
If Block
Inside If

If - Else Statement: When the If - Else conditional statement is used, the Else block of code executes if the condition is False.

a = int(input()) # -1
if a > 0:  
    print("Positive")  
else:  
    print("Not Positive")  

# Output is:
Not Positive

Nested Conditions: The conditional block inside another if/else conditional block is called as a nested conditional block.

if Condition A:
    if Condition B:
        block of code
else:
    block of code

if Condition A:
    block of code
else:
    if Condition B:
        block of code

Elif Statement: Use the elif statement to have multiple conditional statements between if and else. The elif statement is optional.

if Condition A:
    block of code
elif Condition B:
    block of code
else:
    block of code

Identation:

1. Space(s) in front of the conditional block is called indentation. 2. Indentation(spacing) is used to identify the Conditional Blocks. 3. Standard practice is to use four spaces for indentation.

Strings - working with strings

String Concatenation: Joining strings together is called string concatenation.

a = "Hello" + " " + "World"
print(a) # Hello World

String Repetition: * operator is used for repeating strings any number of times as required.

a = "$" * 10
print(a) # $$$$$$$$$$

Length of String: len() returns the number of characters in a given string.

username = input() # Ravi
length = len(username)
print(length) # 4

String Indexing: We can access an individual character in a string using their positions (which start from 0) . These positions are also called index.

username = "Ravi"
first_letter = username[0]
print(first_letter) # R

String Slicing: Obtaining a part of a string is called string slicing. Start from the start_index and stops at the end_index. (end_index is not included in the slice).

message = "Hi Ravi"
part = message[3:7]
print(part) # Ravi

Slicing to End: If end_index is not specified, slicing stops at the end of the string.

message = "Hi Ravi"
part = message[3:]
print(part) # Ravi

Slicing from Start: If the start_index is not specified, the slicing starts from the index 0.

message = "Hi Ravi"
part = message[:2]
print(part) # Hi

Negative Indexing: Use negative indexes to start the slice from the end of the string.

b = "Hello, World!"
print(b[-5:-2]) # orl

Reversing String: Reverse the given string using the extended slice operator.

txt = "Hello World"
txt = txt[::-1]
print(txt) # dlroW olleH

Membership check-in strings:

in: By using the in operator, one can determine if a value is present in a sequence or not.

language = "Python"
result = "P" in language
print(result) # True

not in: By using the, not in operator, one can determine if a value is not present in a sequence or not.

language = "Python"
result = "P" not in language
print(result) # False

Calculations in Python

Addition: Addition is denoted by + sign.

print(2 + 5)  # 7
print(1 + 1.5) # 2.5

Subtraction: Subtraction is denoted by - sign.

print(5 - 2) # 3

Multiplication: Multiplication is denoted by * sign.

print(2 * 5) # 10
print(5 * 0.5) # 2.5

Division: Division is denoted by / sign.

print(80 / 5) # 16.0

Modulus: To find the remainder, we use the Modulus operator %.

print(7 % 2) # 1

Exponent: To find a power b, we use Exponent Operator **.

print(7 ** 2) # 49

Floor division: To find an integral part of the quotient we use Floor Division Operator //.

print(13 // 5) # 2

Input and Output Basics

Take Input From User: input() allows flexibility to take input from the user. Reads a line of input as a string.

username = input() # Ajay

Printing the Output: print() function prints the message to the screen or any other standard output device.

print(username) # Ajay

Comments: Comment starts with a hash # . It can be written in its own line next to a statement of code.

# This is a comment

String Methods

Name	Syntax	Usage
isdigit()	str.isdigit()	Gives True if all the characters are digits. Otherwise, False.
strip()	str.strip()	Removes all the leading and trailing spaces from a string.
strip() with separator	str.strip(separator)	We can also specify separator(string) that need to be removed.
replace()	str.replace(old, new)	Gives a new string after replacing all the occurrences of the old substring with the new substring.
startswith()	str_var.startswith(value)	Gives True if the string starts with the specified value. Otherwise, False.
endswith()	str.endswith(value)	Gives True if the string ends with the specified value. Otherwise, False.
upper()	str.upper()	Gives a new string by converting each character of the given string to uppercase.
lower()	str.lower()	Gives a new string by converting each character of the given string to lowercase.
split()	str.split()	The split() method splits a string into a list.
split() with separator	str.split(separator, maxsplit)	Specifies the separator to use when splitting the string. By default any whitespace is a separator.
join()	str.join(iterable)	The join() method takes all items in an iterable and joins them into one string.

String Formatting: String Formatting simplifies the concatenation. It increases the readability of code and type conversion is not required.

Add Placeholders: Add placeholders {} where the string needs to be formatted.

name = "Raju"
age = 10
msg = "Hi {}. You are {} years old."
print(msg.format(name, age)) # Hi Raju. You are 10 years old.

Numbering Placeholders: Numbering placeholders, will fill values according to the position of arguments.

name = input() # Raju
age = int(input()) # 10
msg = "Hi {1}. You are {0} years old."
print(msg.format(name, age)) # Hi 10. You are Raju years old.

Naming Placeholder: Naming placeholders will fill values according to the keyword arguments.

name = input() # Raju
age = int(input()) # 10
msg = "Hi {name}. You are {age} years old."
print(msg.format(age=age, name=name)) # Hi Raju. You are 10 years old.

Relational & Logical Operators

Relational Operators are used to comparing values. Gives True or False as the result of a comparison.

Operator	Name	Example	Output
>	Is greater than	print(2 > 1)	True
<	Is less than	print(5 < 10)	True
==	Is equal to	print(3 == 4)	False
<=	Is less than or equal to	print(2 <= 1)	False
>=	Is greater than or equal to	print(2 >= 1)	True
!=	Is not equal to	print(2 != 1)	True

Logical operators are used to performing logical operations on Boolean values. Gives True or False as a result.

Name	Code	Output
and	print((5 < 10) and (1 < 2))	True
or	print((5 < 10) or (2 < 2))	True
not	print(not (2 < 3))	False

Logical Operators Truth Table:

A	B	A and B
True	True	True
True	False	False
False	False	False
False	True	False

A	B	A or B
True	True	True
True	False	True
False	False	False
False	True	True

A	Not A
True	False
False	True