The tell() function in Python 🐍

The tell() function returns the current position of the file pointer within the data stream. It is most often used when working with files. 📂

The function does not accept any arguments and returns an integer - the position in bytes from the beginning of the stream. 🔢

with open("file.txt", "rb") as f:
    print(f.tell())

PYTHON SKILL ROADMAP

│
├── 📁 Python Basics
│ ├── 📁 Variables & Data Types
│ ├── 📁 Input & Output
│ ├── 📁 Operators
│ ├── 📁 Conditional Statements
│ └── 📁 Loops

│
├── 📁 Core Python Concepts
│ ├── 📁 Lists
│ ├── 📁 Tuples
│ ├── 📁 Sets
│ ├── 📁 Dictionaries
│ ├── 📁 Strings
│ └── 📁 Functions

│
├── 📁 Problem Solving
│ ├── 📁 Patterns
│ ├── 📁 Number Problems
│ ├── 📁 String Problems
│ ├── 📁 List Problems
│ ├── 📁 Searching
│ └── 📁 Sorting Basics

│
├── 📁 Object-Oriented Python
│ ├── 📁 Classes & Objects
│ ├── 📁 Constructors
│ ├── 📁 Inheritance
│ ├── 📁 Encapsulation
│ ├── 📁 Polymorphism
│ └── 📁 Real OOP Examples

│
├── 📁 File Handling & Errors
│ ├── 📁 Read Files
│ ├── 📁 Write Files
│ ├── 📁 CSV Files
│ ├── 📁 JSON Files
│ ├── 📁 Exception Handling
│ └── 📁 Logging Basics

│
├── 📁 Python Libraries
│ ├── 📁 NumPy Basics
│ ├── 📁 Pandas Basics
│ ├── 📁 Matplotlib Basics
│ ├── 📁 Requests
│ ├── 📁 BeautifulSoup
│ └── 📁 Streamlit Basics

│
├── 📁 Automation Skills
│ ├── 📁 File Organizer
│ ├── 📁 Email Automation
│ ├── 📁 Web Scraping
│ ├── 📁 API Automation
│ ├── 📁 Excel Automation
│ └── 📁 Task Scheduler

│
├── 📁 Backend Basics
│ ├── 📁 Flask Basics
│ ├── 📁 FastAPI Basics
│ ├── 📁 REST APIs
│ ├── 📁 Databases
│ ├── 📁 Authentication Basics
│ └── 📁 Deploy Your API

│
└── 📁 Portfolio Projects
├── 📁 Expense Tracker
├── 📁 Weather App
├── 📁 Web Scraper
├── 📁 URL Shortener
├── 📁 Automation Bot
└── 📁 AI Note Summarizer

Learn the syntax first.
Then solve problems.
Then build projects.

That is how Python starts making sense.

@python_bds

🧠 return vs print() in Python

These are not interchangeable.

def add(a, b):
    print(a + b)

Calling:

result = add(2, 3)

prints:

5

But:

result

is actually:

None

Now compare:

def add(a, b):
    return a + b

This time:

result = add(2, 3)

gives:

result == 5

print() sends something to the screen.
return sends a value back to the caller.

That distinction becomes extremely important once functions start calling other functions.

🐍 Python Performance Optimization

Python Performance Optimization: Make Your Code Faster
Writing Python code that works is only the beginning. For real-world applications, performance matters.

Here are some techniques that can significantly improve Python performance:

⚡️ 1. Use the right data structures
Choosing a set instead of a list for frequent membership checks can dramatically reduce lookup time.
⚡️ 2. Avoid unnecessary loops
Use built-in functions, comprehensions, and optimized libraries such as NumPy when appropriate.
⚡️ 3. Profile before optimizing
Tools like cProfile and timeit help identify the actual bottlenecks instead of optimizing blindly.
⚡️ 4. Reduce unnecessary memory usage
Generators can process large datasets without loading everything into memory at once.
⚡️ 5. Use vectorization for data processing
NumPy operations can be much faster than manually looping through millions of values.

💡 Key principle:
Don't optimize what you haven't measured.

🐛 This Python Bug Looks Random, But It Isn't

Look at this:

functions = []

for i in range(3):
    functions.append(lambda: i)

for f in functions:
    print(f())

What would you expect?

0
1
2

Actual output:

2
2
2

Why? The lambdas don't store the current value of i. They remember the variable i.
By the time the functions are called, the loop has finished and i is 2.

This is called late binding.
If you actually want each function to capture the current value:

functions = []

for i in range(3):
    functions.append(lambda i=i: i)

Now:

0
1
2

This becomes particularly important when creating callbacks inside loops, especially in GUI code, asynchronous code, and event-driven applications.

The bug isn't in lambda. It's in understanding when the variable is looked up.

This Book Explains more than 400 Concepts with codes.

📘 The Big Book of Small Python Projects

✍️ Author: Al Sweigart

🔗 Read Online

#Python #Projects
➖➖➖➖➖➖➖➖➖➖➖
📚 More free programming books → @free_programming_books_bds
Part of @bigdataspecialist community