Python Conditional Statements: if,else and elif

on

Python Conditional Statements: if, else, and elif Explained

1. 🧠 What is if-else in Python?

In Python, if and else are used to make decisions. You can check a condition and run a block of code depending on whether it’s True or False.

🔤 Syntax:


if condition:
    # code to run if condition is True
else:
    # code to run if condition is False

Example 1: Basic if-else


age = 18
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

Output:


You are an adult.

📌 How it works:

  • age >= 18 is the condition.
  • If it's True, the first block runs.
  • If it's False, the else block runs.

2. 🤔 Why Do We Need elif?

Sometimes you want to check multiple conditions — not just one or two. This is where elif (short for "else if") becomes useful.

📘 Example Situation:

Let’s say you want to check if a number is positive, negative, or zero.

3. 🪜 Using if-elif-else

🔤 Syntax:


if condition1:
    # run if condition1 is True
elif condition2:
    # run if condition2 is True
elif condition3:
    # run if condition3 is True
else:
    # run if all above conditions are False

Example 2: Check if number is positive, negative, or zero


num = 0

if num > 0:
    print("Positive number")
elif num == 0:
    print("Zero")
else:
    print("Negative number")

Output:


Zero

📌 How it works:

  • The code checks num > 0. If True, it prints "Positive number".
  • If not, it checks num == 0. If True, it prints "Zero".
  • If both conditions are False, it goes to else.

4. 🧪 More Real-World Example: Grading System


marks = 85

if marks >= 90:
    print("Grade: A+")
elif marks >= 80:
    print("Grade: A")
elif marks >= 70:
    print("Grade: B")
elif marks >= 60:
    print("Grade: C")
else:
    print("Grade: F")

Output:


Grade: A

5. ⚠️ Caution:

  • Only one block of code will run in an if-elif-else chain.
  • Python checks conditions from top to bottom and stops when one is True.

6. ✅ Summary Table

Keyword Use Can be repeated?
if First condition to check Only once
elif More conditions to check if previous ones failed Yes, multiple times
else Runs if all other conditions are False Only once at the end

📌 Final Tip:

Use if-else for two-way decisions, and if-elif-else when you have three or more cases to check. It makes your code cleaner and avoids writing many nested if statements.

Hope this clears your confusion on Python conditions! 🐍🧠

📚 Practice Questions:

📚 Related Topics:

📌 Bookmark this blog or follow for updates!

Python Logo

👍 Liked this post? Share it with friends or leave a comment below!

“In the world of code, Python is the language of simplicity, where logic meets creativity, and every line brings us closer to our goals.”— Only Python

📌 Follow Us And Stay Updated For Daily Updates

📖 More Resources

📚 Python Crash Course Chapter-wise Exercises
📚 AI And MACHINE LEARNING ROADMAP: From Basic to Advanced
    Stage 1: Python & Programming Fundamentals 
    
----------------------------------------
1. Python & Programming Fundamentals
----------------------------------------
1.1 Environment Setup
    • Install Python 3.x, VS Code / PyCharm
    • Configure linting, formatters (e.g., Pylint, Black)
    • Jupyter Notebook / Google Colab basics

1.2 Core Python Syntax
    • Variables, Data Types (int, float, str, bool)
    • Operators: arithmetic, comparison, logical, bitwise
    • Control Flow: if / else / elif
    • Loops: for, while, break/continue

1.3 Functions & Modules
    • Defining functions, return values
    • Parameters: positional, keyword, default args
    • *args, **kwargs
    • Organizing code: modules and packages
    • Standard library exploration (os, sys, datetime, random, math)

1.4 Data Structures
    • Lists, Tuples, Sets, Dictionaries
    • List/dict comprehensions
    • Built-in functions: map, filter, zip, enumerate
    • When to use which structure

1.5 File Handling & Exceptions
    • Reading/Writing text and binary files
    • Context managers (`with` statement)
    • Exception handling: try/except/finally
    • Custom exceptions

1.6 Object-Oriented Programming (OOP)
    • Classes, Instances, Attributes, Methods
    • __init__, self, class vs instance attributes
    • Inheritance, Polymorphism, Encapsulation
    • Magic methods: __str__, __repr__, __add__, etc.
    • Use-cases in structuring larger projects

1.7 Virtual Environments & Package Management
    • venv / pipenv / poetry basics
    • Installing and managing dependencies
    • requirements.txt and environment.yml

🛠 Tools: VS Code, Git for version control, Jupyter/Colab
    Stage 2: Mathematics for Machine Learning 
    
----------------------------------------
2. Mathematics for Machine Learning
----------------------------------------
2.1 Linear Algebra
    • Scalars, Vectors, Matrices, Tensors
    • Operations: addition, multiplication, dot product
    • Matrix properties: transpose, inverse, rank
    • Eigenvalues & Eigenvectors (intuition)
    • Applications: data transformations, PCA

2.2 Calculus
    • Functions and limits (intuitive overview)
    • Derivatives: gradient of single-variable and multi-variable functions
    • Chain rule (key for backpropagation in neural networks)
    • Partial derivatives
    • Basic integration (overview; less often used directly)

2.3 Probability & Statistics
    • Basic probability theory: events, conditional probability, Bayes’ theorem
    • Random variables, distributions (normal, binomial, Poisson, etc.)
    • Descriptive statistics: mean, median, mode, variance, standard deviation
    • Inferential statistics: hypothesis testing, p-values, confidence intervals
    • Sampling methods, bias, variance concepts

2.4 Optimization Basics
    • Concept of optimization in ML (finding minima of loss functions)
    • Gradient descent: batch, stochastic, mini-batch
    • Learning rate intuition

🛠 Tools / References: 
    • Interactive calculators: Desmos, GeoGebra
    • Python libraries: NumPy for experimentation
    Stage 3: Data Handling & Preprocessing 
    
----------------------------------------
3. Data Handling & Preprocessing
----------------------------------------
3.1 NumPy Essentials
    • ndarrays: creation, indexing, slicing
    • Vectorized operations vs Python loops
    • Broadcasting rules
    • Random number generation

3.2 Pandas for Tabular Data
    • Series & DataFrame: creation and basic ops
    • Reading data: CSV, Excel, JSON
    • Indexing, selection (loc/iloc), filtering rows
    • Handling missing values: dropna, fillna
    • Detecting/removing duplicates
    • Combining datasets: merge, join, concat
    • GroupBy operations, aggregation, pivot tables

3.3 Feature Engineering
    • Feature scaling: normalization (Min-Max), standardization (Z-score)
    • Encoding categorical variables: one-hot, ordinal encoding
    • Date/time feature extraction (if applicable)
    • Creating new features via domain knowledge
    • Feature selection: variance threshold, correlation analysis

3.4 Data Visualization
    • Matplotlib basics: line plot, scatter plot, histograms, bar charts
    • Seaborn overview: higher-level plots (heatmap, pairplot)
    • Visualizing distributions, relationships, outliers
    • Plot customization: titles, labels, legends

3.5 Handling Real-World Data Challenges
    • Imbalanced datasets: oversampling (SMOTE), undersampling, class weights
    • Outlier detection and treatment
    • Data leakage awareness
    • Pipeline creation in scikit-learn

🛠 Tools: NumPy, Pandas, Matplotlib, Seaborn, scikit-learn utilities
    Stage 4: Core Machine Learning 
    
----------------------------------------
4. Core Machine Learning
----------------------------------------
4.1 ML Concepts & Workflow
    • What is ML? Supervised vs Unsupervised vs Semi-supervised vs Reinforcement
    • Training, Validation, Testing splits
    • Overfitting vs Underfitting, bias-variance trade-off
    • Cross-validation techniques: k-fold, stratified

4.2 Supervised Learning: Regression
    • Linear Regression: assumptions, cost function, normal equation
    • Regularized Regression: Ridge, Lasso, Elastic Net
    • Polynomial Regression
    • Evaluation metrics: MSE, RMSE, MAE, R²

4.3 Supervised Learning: Classification
    • Logistic Regression: sigmoid, decision boundary, loss
    • k-Nearest Neighbors (KNN)
    • Decision Trees: entropy/gini, pruning
    • Ensemble Methods:
        - Bagging: Random Forest
        - Boosting: AdaBoost, Gradient Boosting, XGBoost (intro)
    • Support Vector Machines (SVM): kernel trick overview
    • Naive Bayes: Gaussian, Multinomial
    • Evaluation: accuracy, precision, recall, F1-score, ROC-AUC
    • Confusion matrix analysis

4.4 Unsupervised Learning
    • Clustering:
        - K-Means: elbow method, silhouette score
        - Hierarchical clustering: dendrograms
        - DBSCAN
    • Dimensionality Reduction:
        - PCA: variance explained
        - t-SNE / UMAP (visualization-focused)
    • Anomaly Detection overview

4.5 Model Selection & Tuning
    • Hyperparameter tuning: grid search, random search, Bayesian optimization (overview)
    • Automated tuning libraries (e.g., scikit-learn’s GridSearchCV, RandomizedSearchCV)
    • Pipeline building to avoid leakage
    • Feature importance and model interpretability basics

🛠 Tools: scikit-learn, pandas, NumPy
    Stage 5: Deep Learning Foundations 
    
----------------------------------------
5. Deep Learning Foundations
----------------------------------------
5.1 Neural Network Basics
    • Artificial neuron model, activation functions (ReLU, Sigmoid, Tanh)
    • Architecture: input, hidden, output layers
    • Forward propagation, loss functions (Cross-entropy, MSE)
    • Backpropagation: gradient computation, chain rule

5.2 Deep Learning Frameworks
    • TensorFlow & Keras: Sequential and Functional APIs
    • PyTorch basics: tensors, autograd, nn.Module
    • Comparing TF/Keras vs PyTorch (choose one to start)

5.3 Training Deep Models
    • Optimizers: SGD, Adam, RMSprop
    • Learning rate scheduling
    • Regularization: Dropout, Batch Normalization, Weight Decay
    • Handling overfitting: early stopping, data augmentation

5.4 Basic DL Projects
    • MNIST digit classification
    • CIFAR-10 image classification (small CNN)
    • Simple feedforward network on tabular data

🛠 Tools: TensorFlow/Keras or PyTorch, GPU if available (Colab/GPU runtime)
    Stage 6: Advanced Deep Learning & Architectures 
    
----------------------------------------
6. Advanced Deep Learning & Architectures
----------------------------------------
6.1 Convolutional Neural Networks (CNNs)
    • Convolution operations, filters, feature maps
    • Pooling layers, padding, stride
    • Famous architectures overview: LeNet, AlexNet, VGG, ResNet (intuition)
    • Transfer Learning: fine-tuning pre-trained models

6.2 Recurrent Neural Networks (RNNs) & Sequence Models
    • RNN basics: hidden states, vanishing gradients
    • LSTM, GRU: gating mechanisms
    • Sequence-to-sequence models (intro)
    • Attention mechanism: intuition

6.3 Transformers & Attention
    • Self-attention mechanism
    • Transformer architecture: encoder, decoder overview
    • Pre-trained transformer models: BERT, GPT family (conceptual)
    • Fine-tuning transformers for tasks

6.4 Generative Models
    • Autoencoders: basic, variational autoencoders (VAE) overview
    • Generative Adversarial Networks (GANs): generator/discriminator intuition
    • Applications and basic experiments

6.5 Advanced Techniques
    • Multi-task learning, meta-learning (intro)
    • Few-shot learning, transfer learning deeper dive
    • Neural architecture search (overview)
    • Model compression, pruning, quantization (deployment considerations)

🛠 Tools: TensorFlow / PyTorch, Hugging Face Transformers library
    Stage 7: Natural Language Processing (NLP) Advanced 
    
----------------------------------------
7. Natural Language Processing (NLP)
----------------------------------------
7.1 Text Preprocessing & Representation
    • Tokenization (word, subword/BPE)
    • Stopwords removal, lemmatization vs stemming
    • Word embeddings: Word2Vec, GloVe, FastText
    • Contextual embeddings: ELMo, BERT embeddings

7.2 Transformer-based NLP
    • Pre-trained models: BERT, RoBERTa, GPT, T5
    • Fine-tuning for classification, QA, summarization
    • Sequence generation tasks using GPT-like models

7.3 Specialized NLP Tasks
    • Named Entity Recognition (NER)
    • Machine Translation overview
    • Question Answering pipelines
    • Text Summarization (extractive vs abstractive)
    • Sentiment Analysis deep dive

7.4 Evaluation Metrics in NLP
    • BLEU, ROUGE, METEOR (for generation)
    • Accuracy, F1 for classification tasks

🛠 Tools: Hugging Face Transformers, spaCy, NLTK
    Stage 8: Computer Vision Advanced 
    
----------------------------------------
8. Computer Vision (CV)
----------------------------------------
8.1 Image Preprocessing & Augmentation
    • OpenCV basics: reading, resizing, color conversions
    • Data augmentation techniques: flips, rotations, crops, color jitter

8.2 Advanced CNN Architectures
    • Inception, ResNet, DenseNet, EfficientNet (conceptual)
    • Transfer learning and fine-tuning advanced models
    • Object detection frameworks: YOLOvX, SSD, Faster R-CNN (overview)
    • Semantic segmentation: U-Net, Mask R-CNN
    • Instance segmentation concepts

8.3 Vision Transformers (ViT)
    • Applying transformer concepts to images
    • Fine-tuning ViT for classification

8.4 Specialized CV Tasks
    • Face recognition pipelines
    • Video analysis basics: action recognition, object tracking
    • 3D vision intro (depth estimation)

🛠 Tools: OpenCV, TensorFlow/PyTorch, libraries like Detectron2 or YOLO implementations
    Stage 9: Reinforcement Learning & Advanced Topics 
    
----------------------------------------
9. Reinforcement Learning & Advanced Topics
----------------------------------------
9.1 Reinforcement Learning Foundations
    • Markov Decision Process (MDP)
    • Value functions, policy functions
    • Q-Learning, SARSA (tabular methods)
    • Exploration vs Exploitation

9.2 Deep Reinforcement Learning
    • Deep Q-Networks (DQN)
    • Policy Gradient Methods: REINFORCE, Actor-Critic
    • Advanced: A3C, PPO, DDPG overview

9.3 Other Advanced AI Topics
    • Graph Neural Networks (GNNs): node/graph embeddings (overview)
    • Time Series Forecasting with ML/DL: RNN/LSTM, Prophet intro
    • Bayesian Methods overview
    • AutoML and neural architecture search concepts
    • Federated Learning basics (privacy-aware training)
    • MLOps fundamentals:
        - Model versioning
        - Continuous integration/continuous deployment (CI/CD) for ML
        - Monitoring models in production
        - Tools: MLflow, Kubeflow (intro)
    • Edge AI / TinyML overview (deploying models on devices)

🛠 Tools: RL libraries (Stable Baselines3), MLflow, Kubernetes intro, Docker
    Stage 10: Deployment, Production & MLOps 
    
----------------------------------------
10. Deployment, Production & MLOps
----------------------------------------
10.1 Model Serving & APIs
    • REST API with Flask / FastAPI
    • gRPC basics (overview)
    • Dockerizing ML applications
    • Serving with TensorFlow Serving or TorchServe

10.2 Cloud Deployment
    • Deploy on AWS Sagemaker / GCP AI Platform / Azure ML (basic workflow)
    • Serverless deployments (AWS Lambda, Cloud Functions) for small models
    • CI/CD pipelines for ML: GitHub Actions or Jenkins integration

10.3 Monitoring & Maintenance
    • Logging model inputs/outputs
    • Drift detection (data/model drift)
    • Retraining pipelines (automated or scheduled)
    • Scaling considerations

10.4 MLOps Tools & Practices
    • Experiment tracking (MLflow, Weights & Biases)
    • Data versioning (DVC)
    • Model registry concepts
    • Infrastructure as Code (Terraform intro)

🛠 Tools: Docker, Kubernetes basics, CI/CD tools, cloud consoles
    Stage 11: Real-World Projects & Portfolio 
    
----------------------------------------
11. Real-World Projects & Portfolio
----------------------------------------
11.1 Project Ideas by Domain
    • Tabular Data: Predictive analytics (e.g., churn prediction)
    • NLP: Chatbot, summarizer, translation prototype
    • CV: Image classifier, object detector, image segmentation app
    • Time Series: Forecasting stock or weather data
    • RL: Simple game-playing agent
    • Generative: GAN art generation or style transfer demo

11.2 End-to-End Pipeline
    • Data collection & preprocessing
    • Model training & validation
    • Deployment as API or web app (Streamlit/Flask)
    • Monitoring & iteration
    • Documentation & README

11.3 Collaboration & Open Source
    • Participate in Kaggle competitions (beginner → intermediate)
    • Contribute to open-source ML projects
    • Write blog posts/tutorials documenting your projects

11.4 Soft Skills & Communication
    • Clear README, code comments
    • Presentation slides or videos of project demos
    • Networking: sharing work on LinkedIn, GitHub

🛠 Tools: GitHub Pages, Streamlit, Heroku/Netlify, Docker
    Stage 12: Ethics, Explainability & Continuous Learning 
    
----------------------------------------
12. Ethics, Explainability & Continuous Learning
----------------------------------------
12.1 AI Ethics & Responsible AI
    • Bias & Fairness: identifying and mitigating bias
    • Privacy concerns: GDPR, data protection best practices
    • Transparency: documenting data sources and model decisions

12.2 Explainable AI (XAI)
    • Model interpretability: SHAP, LIME (basic usage)
    • Interpreting black-box models vs inherently interpretable models
    • Communicating explanations to stakeholders

12.3 Continuous Learning & Staying Updated
    • Following research: arXiv alerts, ML conferences (NeurIPS, ICML, CVPR summaries)
    • Blogs, podcasts, newsletters (e.g., “The Batch” by deeplearning.ai)
    • Reading codebases of popular libraries, exploring new architectures
    • Community involvement: forums, study groups

12.4 Advanced Research Topics (Optional/For Aspirants)
    • Research paper reading workflow
    • Experimentation frameworks
    • Contributing to academic research or advanced industrial research

🛠 Tools: arXiv, Google Scholar alerts, RSS readers, community forums

Comments

Post a Comment