Intro to Python

CSCI 344: Advanced Web Technologies

Spring 2025

Outline

• Installing and configuring Python
• Python Crash Course
• Practice

Outline

• Installing and configuring Python + Poetry
• Python Crash Course
• Practice

Installing Python

You will need to install python to build your server. Here is the documentation for doing it.

• Install Python: https://www.python.org/downloads/
• Getting the Python path to work on Windows

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If you already have python installed on your computer, make sure your version is at least 3.8. If it isn’t you’ll need to upgrade your python installation.

Installing Poetry

You will also need to install Poetry, which is analogous to npm.

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• Instructions here: https://python-poetry.org/docs/#installing-with-the-official-installer

Outline

• Installing and configuring Python
• Python Crash Course
• Practice

Comments

'''

There are two ways to do comments. For longer

comments, please feel free to use the "docstring"

notation: three quotes at the beginning of the

comment, three quotes at the end.

'''

​

# use the pound sign for smaller comments!

​

7

Data Types

Data Primitives

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Type Example

Integer (int) 1, 555, -1000000

Float (float) 2.567, 3.14159

String (string) 'Hello world!'

Boolean (bool) True, False

None empty variable

In Python, the most basic data types are:

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Strings & String Functions

‘My string’.lower() # returns a copy of the string that is all lowercase

‘My string’.upper() # returns a copy of the string that is all uppercase

‘My string’.replace(‘ ‘, ‘_’) # returns a copy of the string where the instances of the

first argument are replaced by the second argument

‘My string’.find(‘s’) # returns the position where the first instance of the

argument is found. Returns -1 if argument not found

‘Hello {0}’.format('Walter') # allows you to format and inject data into a string

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More here: https://docs.python.org/3/library/stdtypes.html#string-methods

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Lists

A list is a mutable sequence of values:

� list_of_strings = ['freshman', 'sophomore', 'junior', 'senior']�

Useful for organizing and conveniently accessing related data

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List Methods

• Detecting the length of a list:�len(my_list)
• Indexing a list:�my_list[0]
• Appending an element to a list:�my_list.append('some value')
• Removing an element from a list (from the bottom):�my_list.pop()

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Dictionaries

# two ways to create a dictionary:�my_dict = dict(a=123, b=456)�my_dict = {'a': 123, 'b': 456}

# access an item by its key:�my_dict.get('a') my_dict['a']

# add a new item to a dictionary:�my_dict['c'] = 789

# iterate through a dictionary:�for key in my_dict:� print(key, my_dict.get(key))

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Dictionaries and JSON

Dictionaries are easily converted to and from JSON using the built-in JSON module:

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import json

json.dumps(my_dict) # converts a Python dictionary into a JSON string

json.loads(json_string) # convert a JSON string into a dictionary

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Variables

Declaring Variables

Officially, variable names in Python can be any length and can consist of uppercase and lowercase letters (A-Z, a-z), digits (0-9), and the underscore character (_). An additional restriction is that, although a variable name can contain digits, the first character of a variable name cannot be a digit.

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401k_account = 'Z346rgGX' # illegal

account_401k = 'Z346rgGX' # OK

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You don’t declare a type when creating a variable. Type is determined when you assign.

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Source: https://realpython.com/python-variables/

Naming Variables

Although Python doesn’t care what you name your variables (beyond the rules specified in the previous slide), there are some conventions that most people follow:�

1. Ensure your variable names are mnemonic
2. “Snake case” for functions and variable names
1. first_name = 'Beyonce'
2. last_name = 'Knowles'
3. “Snake case” for file names too: hello_world.py
4. Python is case-sensitive

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Source: https://realpython.com/python-variables/

Naming Variables: Snake Case

Functions

def divide_two_nums(num, denom):� return num / denom

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def move_avatar_left(dog):� dog.x -= 1� dog.redraw()

Variables

time_left_til_end_of_class = 35

first_name = 'Jazmin'

last_name = 'Morales'

Examples of snake case variables and functions:

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Reserved words

When naming variables, you aren’t allowed to use reserved words. The following words have special meanings in Python.

and del global not with� as elif if or yield� assert else import pass False� break except in raise None� class finally is return True� continue for lambda try� def from nonlocal while

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Operators

Arithmetic Operators

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�

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Comparison Operators

Comparison operators compare two operands according to a comparison rule and evaluate to either True or False (boolean)

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Logical Operators

Logical operators provide additional ways to determine whether something is true or false:

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Functions

Some useful built-in functions

• Outputting information — print()
• Asking for information from a user — input()
• Converting between data types — int(), float(), bool(), and str()

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def name_of_function(parameters):

statement(s)

return some_value

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Example: Function with type hints

def add_em(num_1: float, num_2: float) -> int:

return num_1 + num_2

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# call / invoke the function

result = add_em(33, 44)

print('The sum is:', result)

• Indentation matters (4 spaces per “level”)
• Type hints are suggestions, but they’re not enforced

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Functions can have required and optional parameters

# defining the function

def say_hello(name: str, time_of_day: str='morning'):

print('Hello there,' + name + '!')

print('How are you this ' + time_of_day + '?')

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# calling (invoking) the function

say_hello('Varun')

say_hello('Grace', time_of_day='evening')

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Things that your interpreter doesn’t care about (but that you should): Type Hints

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1. Type Hints: Python doesn’t care whether or not your function signature has a data_type, but it’s *very useful for code readability:

def say_hello(name, time_of_day='morning'):

...

�def say_hello(name: str, time_of_day: str='morning'):

...�

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Things that your interpreter doesn’t care about (but that you should): Docstrings

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2. Docstrings: a way of documenting your code. Useful for helping others who might use your function later on; and also about helping your future self out when you revisit this code...wait...what did this do again?

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Things that your interpreter doesn’t care about (but that you should): Docstrings

def add_em(num_1: float, num_2: float):

'''

Adds two numbers together.

Args:

num_1(float): the first number in the addition operation.

num_2(float): the second number in the addition operation.

Returns:

float: the sum of the two numbers

'''

return num_1 + num_2

​

31

Control & “Truthiness”

Truthiness → Things that evaluate to True?

if True:

print('True always evaluates to True')

if 1:

print('1 also evaluates to True')

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if 'Walter':

print('any non-null or non-False value also evaluates to True')

33

What evaluates to False?

if False:

# will not execute

print('False always evaluates to False')

if 0:

# will not execute

print('0 always evaluates to False')�

if None:

# will not execute

print('None always evaluates to False')

​

​

34

...more ways to be True...

if not False:

print('not False always evaluates to True')

if not 0:

print('not 0 always evaluates to True')

if not None:

print('not None always evaluates to True')

​

​

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...more ways to be True...

# expressions and other operators can also be part of a conditional:

def check_password(password:str, username:str):

# some logic...

return True

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if check_password('12345678', 'tylan98'):

print('Login...')

else:

print('Try again...')

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36

...more ways to be True...

my_list = [1, 2, 3]

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so this...

if len(my_list) != 0:

print('Not empty!')

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...does the same thing as...

if my_list:

print("Not empty!")

​

37

If / Elif / Else Example:

1. def give_grade(score):

2. if (score >= 90):

3. return 'A'

4. elif score >= 80:

5. return 'B'

6. elif score >= 70:

7. return 'C'

8. elif score >= 60:

9. return 'D'

10. else:

11. return 'F'

​

38

While Loops & For Loops

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# while loop:

counter = 0

while counter < len(names):

print(names[counter])

counter += 1

# for loop:

for name in names:

print(name)

names = ['Seamus', 'Millie', 'Scout', ‘Froggie', 'Lucy', 'Bagel']

For Loops + Range Function

for i in range(10):� print(i)

Range Function

Range functions help you to conveniently generate a list of numbers. This details of the range function are elaborated here.

range(10)�Generates a sequence from 0 to 9 (excludes last number)

range(5, 10)�Generates a sequence from 5 to 9 (excludes last number)

range(2, 30, 3)�Generates a sequence from 2 to 30, incrementing by 3 each time

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Classes & Objects

class User:

def __init__(self, name, age):

self.name = name

self.age = age

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def displayGreeting(self):

print(f'Welcome {self.name}')

_______________________________________________________________________

person1 = User('Shirly', 67)

person2 = User('Walter', 67)

person1.displayGreeting()

person2.displayGreeting()

Practice Time!

Please download the lecture19 files