Course Introduction Intro To Programming And The Python Language Variables Conditionals Jupyter Notebook And IDLE

Characteristics of Python:

• High-level language (i.e., more abstracted from lower-level details of the computer)

• OOP language

• Interpreted language (i.e., does not need to be compiled from one language to another)

  • One side effect of being interpreted is that the lack of compilation to another language can mean less automatic error checking, so more onus on you to ensure code is bug-free

• Open source

Common use cases of Python:

• AI (e.g., NLP or machine learning)

• Web dev

• Data analysis & visualization

• Desktop GUIs

• Game dev

Print command

print has a few useful arguments called end and sep.

end allows you to specify how the string should end when printed (default is ):

print('Hello,', end = ' ')
print('Dan')
# Prints "Hello, Dan"

sep defines if there is a character between string arguments (default is empty string or single space):

print('Hello', 'Dan', sep = ', ')
# Prints "Hello, Dan"

Basic data types

• int is a mathematical integer

• float is a number with a decimal point

Note: The type function can very quickly tell you what data type a value is.

Arithmetic operators

Operators are the same with a few unique exceptions:

• Addition +

• Subtraction -

• Multiplication *

• Division /

• Integer division //

  • Returns the number of full divisions, discarding the fractional part of the result

• Exponentiation **

• Modulus %

Booleans

Boolean values are True and False.

Comparison operators are the same:

• Equal ==

• Not equal != <>

• Less than and greater than < >

• Less than or equal as well as greater than or equal <= >=

Boolean operators are:

• and

• or

• not

Note: All objects can be casted to a boolean via the bool function.

Strings

When concatenating strings, Python requires that the inputs are all strings, so it doesn't automatically cast the values to strings for you.

# This doesn't work
"4 / 3 = " + (4 / 3)

Note: An alternative way of combining strings is using the str.format method. (See docs for more details.)

Casting

Here are some useful casting functions to convert data types into other data types:

• bool

• int

• str

Python scripts

Also called a module.

Variables

All variables are re-assignable (not immutable):

x = 1
x = 2
print(x) # 2

Syntactic sugar for doing arithmetic at the same time as a re-assignment are:

• +=

• -=

• *=

To dynamically set a variable using a user's input in a CLI, you have the input function:

const name = input("What is your name? ")

Control flow

This is the basic syntax of if, else if, and else control flow:

if x == 2:
  # Execute first success case
elif x === 3:
  # Execute second success case
else:
  # Execute fallback case

Checking errors

Catching errors is just about using a try/except/else flow:

number = input('Please put in a number: ')

# Try to cast the number (could be "100" or "one hundred")
try:
  number = int(number)
# If casting fails, catch the error
except ValueError as e:
  print('Your input was not a number.')
  print(e)
# If casting succeeds, move forward
else:
  print('You input a number!', str(number))

Note: else clause is optional!

You may have noticed ValueError in the example above. Here are some of Python's most common types of errors:

• SyntaxError

• IndentationError

• AssertionError (assertion failed in tests)

• ValueError (function received inappropriate value)

• NameError (invalid variable name used)

• TypeError (function received inappropriate data type)

• IndexError (index out of range in list)

• KeyError (key not found in dictionary)

• MemoryError (operation runs out of memory)

• ZeroDivisionError (attempted to illegally divide a number by zero)