🐍 Python Basic

Note

The only way to learn a new programming language is by writing programs in it. - Dennis Ritchie (inventor of C programming language)

Running Python

Running Python in VS Code

1. To open the ece487_wksp folder in VS Code, right-click on it and choose Open with Code from the menu.

2. To open the Terminal window, go to View and click on Terminal.

3. Type in python and press Enter

4. This will launch the Python Shell, where you can input code and see the output. The Shell acts as a sandbox, allowing you to try out code snippets and get immediate feedback. For example, in the Shell, type 2+3 and press Enter, and it will display 5 on the next line.

5. Try the following code in the Shell:

   2+3
   "hello"+" world"
   a = 2
   print(a)
   

6. The Python Shell behaves like a calculator, allowing you to perform various mathematical operations.

7. Now, try the follownig code:

   2+2    # add two integers
   2+2.0  # add an integer to a floating point number
   2*3    # 2 times 3
   2**2   # 2 squared
   2**3   # 2 cubed
   2**128 # Unlike C, integers in Python does not have a size limitation.    
   2/3    # It returns 1 in C, but 0.6666666666666 in Pyton 
   2/3.0  # Same as 2/3 in Python.
   2//3   # modulo (remainder), same as 2%3 in C
   4//3   # modulo (remainder), same as 4%3 in C
   

8. To exit the Python Shell, type exit() and press Enter, or use Ctrl+z and press Enter.

Running Python in Command Prompt

1. Open Command Prompt or PowerShell (or Terminal on Mac and Ubuntu), and run python on Windows or python3 on Mac.

2. This will open the Python Shell.

Python Programming

Variables

• Numeric types: int, float, long, complex

• String: str

• Boolean: bool (True/False)

Python’s simple types are summarized in the following table:

Python Scalar Types

Type	Example	Description
str	x = 'abc'	String: characters or text
int	x = 1	integers (whole numbers)
float	x = 1.0	floating-point numbers (real numbers)
complex	x = 1 + 2j	Complex numbers (real and imaginary part)
bool	x = True	Boolean: True/False values
NoneType	x = None	Special object indicating nulls

• Use the type() function to find the type for a value or variable

  # String
  c = 'hello'
  print(type(c))
  
  # Integer
  a = 1
  print(type(a))
  
  # Float
  b = 1.0
  print(type(b))
  
  # Boolean
  d = True
  print(type(d))
  
  # None
  e = None
  print(type(e))
  
  # Cast integer to string
  print(type(str(a)))
  
  

Math Operators

• +, -, *, and /

• Exponentiation: **

• Modulo (Remainder): %

Logic Operators

```python
x == y # x is equal to y
x != y # x is not equal to y
x > y # x is greater than y
x < y # x is less than y
x >= y # x is greater than or equal to y 
x <= y # x is less than or equal to y
```

• Try the following code in Python Console.

  2+2
  2+2.0
  2*3
  2**3   # exponentiation 
  2**128 
  2/3
  2/3.0
  2//3   # integer division
  4//3   
  2%3    # modulo
  4%3
  bin(5|2) # convert a number to binary after bit operations
  bin(5^1)
  bin(5&1)
  a = 6
  b = 7
  print(a==6)   # boolean expressions
  print(a==7)
  print(a==6 and b==7)
  print(a==6 or b==6)
  print(not a==6 and b==6)
  print(not (a==6 and b==6))
  

Working with Variables

1. In Python, variables store values like strings or numbers. Strings are blocks of text, such as "Stan Baek is the legendary pirate captain." Numbers can be integers or decimals.

2. Try the the following code in Python Console.

   # a string variable
   name = "Stan Baek"
   

3. You can check the type in use by issuing the type() command

   type(name)
   

4. It will return <class 'str'>

5. Add another string variable:

   title = "the legendary pirate captain"
   

6. You can concatenate strings using + operator:

   character = name + ": " + title
   print(character)  # It will print "Stan Baek: the legendary pirate captain"
   

7. Now, try combining a string with an integer:

   # Integer variable
   age = 726
   # This will raise an error
   print(character + age)
   

8. Convert the integer to a string for proper concatenation:

   print(character + " is " + str(age) + " years old.")
   

9. This will print

   Stan Baek: the legendary pirate captain is 726 years old.
   

10. You can also request input from the user:

    age = input("How old are you? ")
    print(type(age))
    
    # Since age is a string variable. We need to convert it to integer.
    age = int(age)
    
    # Floating-point numbers
    x = 3.141
    print(type(x))
    print(x)  # Prints 3.141
    print(int(x))  # Prints 3
    

11. When creating variables, remember that single or double quotes can be used for strings, but be consistent with your choice.

Functions and Modules

1. Python has many built-in functions. For example:

   name = "Stan Baek"
   len(name)  # Returns the lenght of the string
   type(name) # Returns the type of the variable
   

2. To explore more built-in functions, visit Python’s built-in functions documentation. You can also use the help() function to get descriptions:

   help(len)
   

3. You can define your own functions in Python:

   def add(a, b):
       return a+b
   print(add(3, 4))  # Outputs 7
   

Python Modules

1. You can add extra functionality to Python by importing modules. Modules are collections of additional functions built by others. For example, to access advanced mathematical functions, you can import the math module:

   import math
   print(math.sqrt(16))    # Outputs 4.0
   print(math.sin(math.pi/2))  # Outputs 1.0
   print(math.cos(0))  # Outputs 1.0
   

2. In Python, it’s a convention to import all required modules at the top of the script. This ensures all dependencies are loaded before they’re used and makes the code easier to understand. You can also import specific functions from a module:

   from math import sqrt, sin, pi
   print(sqrt(16))
   print(sin(pi/2))
   

3. We can also import individual functions from a module

   from math import sqrt, sin, pi
   print(sqrt(16))
   print(sin(pi/2))
   cos(0)   # error because cos was not imported
   

4. You can also use an alias for a module:

   import math as m
   m.sqrt(16)
   m.sin(m.pi/2)
   

Conditional Statements

1. The if, else, and elif statements control the flow of execution based on conditions. The basic syntax is:

   if expression:
       statements
   elif expression:
       statements
   else:
       statements
   

2. If no action is needed for a certain condition, you can use the pass statement:

   if expression:
       pass       # Do nothing.
   else:
       statements
   

3. Example:

   word = input("Enter a four-letter word: ")
   if len(word) == 4:
       print(word, "is a four-letter word. Well done.")
   elif len(word) == 3:
       print(word, "is a three-letter word.")
   else:
       print(word, "is not a four-letter word.")
   

Loops

1. Let’s start with a simple while statement.

   x = 1
   while x < 5:
       print(x)
       x = x + 1
   

2. We can use break to exit a loop:

   while True:
       print(x)
       x -= 1
       if x == 0:
           break
   

3. The for loop is commonly used in Python:

   for i in [0, 1, 2, 3, 4]:
       print(i)
   

4. We can also use range():

   for i in range(5):  # Loops through 0 to 4
       print(i)