Python Essentials: Fundamentals for Agents

Why Python?

Python is common in AI/ML and scripting:

• Readable syntax


• Rich ecosystem


• AI/ML libraries


• Good for automation

Basic Syntax

Variables

name = "Alice"
age = 30
price = 19.99
active = True
nothing = None

Print

print("Hello")
print(f"Name: {name}, Age: {age}")

Comments

# Single line comment

"""
Multi-line
comment/docstring
"""

Data Types

Strings

s = "Hello, World"
s.lower()          # "hello, world"
s.upper()          # "HELLO, WORLD"
s.split(", ")      # ["Hello", "World"]
s.replace("o", "0") # "Hell0, W0rld"
s.startswith("He") # True
len(s)             # 12

# F-strings
name = "Alice"
f"Hello, {name}!"  # "Hello, Alice!"

Numbers

x = 10
y = 3
x + y   # 13
x - y   # 7
x * y   # 30
x / y   # 3.333...
x // y  # 3 (integer division)
x % y   # 1 (modulo)
x ** y  # 1000 (power)

Lists

items = [1, 2, 3, 4, 5]
items[0]           # 1
items[-1]          # 5
items[1:3]         # [2, 3]
items.append(6)    # [1, 2, 3, 4, 5, 6]
items.pop()        # 6, items = [1, 2, 3, 4, 5]
len(items)         # 5
3 in items         # True

Dictionaries

user = {
    "name": "Alice",
    "age": 30
}
user["name"]       # "Alice"
user.get("email")  # None
user.get("email", "n/a")  # "n/a"
user["email"] = "a@b.com"
user.keys()        # dict_keys(['name', 'age', 'email'])
user.values()      # dict_values(['Alice', 30, 'a@b.com'])

Sets

s = {1, 2, 3}
s.add(4)           # {1, 2, 3, 4}
s.remove(1)        # {2, 3, 4}
2 in s             # True

Tuples

point = (10, 20)
x, y = point       # Unpacking

Control Flow

If/Elif/Else

if age < 18:
    print("Minor")
elif age < 65:
    print("Adult")
else:
    print("Senior")

For Loops

for item in items:
    print(item)

for i in range(5):
    print(i)  # 0, 1, 2, 3, 4

for i, item in enumerate(items):
    print(f"{i}: {item}")

While Loops

count = 0
while count < 5:
    print(count)
    count += 1

Comprehensions

# List comprehension
squares = [x**2 for x in range(10)]

# With condition
evens = [x for x in range(10) if x % 2 == 0]

# Dict comprehension
squared = {x: x**2 for x in range(5)}

Functions

Basic Function

def greet(name):
    return f"Hello, {name}!"

greet("Alice")  # "Hello, Alice!"

Default Arguments

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

greet("Alice")              # "Hello, Alice!"
greet("Alice", "Hi")        # "Hi, Alice!"

Args and Kwargs

def func(*args, **kwargs):
    print(args)    # Tuple of positional args
    print(kwargs)  # Dict of keyword args

func(1, 2, 3, a=4, b=5)

Lambda

square = lambda x: x ** 2
square(5)  # 25

# Often used with map/filter
list(map(lambda x: x*2, [1, 2, 3]))  # [2, 4, 6]

Classes

Basic Class

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email
    
    def greet(self):
        return f"Hello, I'm {self.name}"

user = User("Alice", "alice@example.com")
user.greet()  # "Hello, I'm Alice"

Inheritance

class Admin(User):
    def __init__(self, name, email, level):
        super().__init__(name, email)
        self.level = level

File Operations

Reading

with open("file.txt", "r") as f:
    content = f.read()

# Or line by line
with open("file.txt", "r") as f:
    for line in f:
        print(line.strip())

Writing

with open("file.txt", "w") as f:
    f.write("Hello, World!")

JSON

import json

# Parse
data = json.loads('{"name": "Alice"}')

# Stringify
text = json.dumps({"name": "Alice"})

# File
with open("data.json") as f:
    data = json.load(f)

with open("data.json", "w") as f:
    json.dump(data, f)

Error Handling

try:
    result = risky_operation()
except ValueError as e:
    print(f"Value error: {e}")
except Exception as e:
    print(f"Error: {e}")
finally:
    cleanup()

Common Modules

import os
os.getcwd()                    # Current directory
os.path.exists("file.txt")     # Check existence
os.environ.get("HOME")         # Environment variable

import sys
sys.argv                       # Command line arguments

import datetime
datetime.datetime.now()        # Current time

import re
re.match(r"\d+", "123abc")     # Regex

import requests  # External
response = requests.get("https://api.example.com")

Pythonic Patterns

Truthiness

if items:           # Non-empty list is truthy
    process(items)

if not name:        # Empty string is falsy
    name = "default"

Ternary

status = "active" if user.active else "inactive"

Unpacking

first, *rest = [1, 2, 3, 4]  # first=1, rest=[2,3,4]
a, b = b, a  # Swap

Context Managers

with open("file.txt") as f:
    # f is automatically closed after

Conclusion

Python essentials:

• Clean, readable syntax


• Rich built-in types


• Powerful comprehensions


• Simple class model


• Great for scripting and automation

Master these basics for effective Python work.

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