Data Science

Building a Sentiment Analysis Model with PyTorch

Published: 2nd June, 2023

Harshini Bhat

Data Science Consultant at almaBetter

Discover the basics of transformers and their advantages over traditional models, as well as the step-by-step process for building a sentiment analysis model.

In today's world, social media and online reviews play a vital role in shaping the perception of individuals and businesses. Sentiment analysis, or opinion mining, is extracting and analyzing opinions and emotions expressed in text data. Sentiment analysis can help businesses and individuals understand the sentiment of their customers and make data-driven decisions.


Sentiment analysis is crucial in social media and online reviews because it helps individuals and businesses understand how customers perceive their products or services. It enables them to identify negative feedback and improve their products or services to enhance customer satisfaction.


sentiment analysis

Pretrained transformers are a powerful tool for sentiment analysis. They are pre-trained neural network models that can be fine-tuned to perform specific natural language processing tasks, such as sentiment analysis. As a result, pretrained transformers can achieve state-of-the-art results in sentiment analysis, making them a popular choice for both businesses and researchers.

What are Transformers?

Transformers are a type of deep learning model that has gained much attention recently due to their outstanding performance in Natural Language Processing (NLP) tasks. Unlike traditional models like recurrent neural networks (RNNs) and convolutional neural networks (CNNs), which process data sequentially or hierarchically, transformers can simultaneously process the entire input sequence. This allows them to capture long-range dependencies and produce more accurate results.

Comparison with other models like RNNs and CNNs

At a high level, transformers rely on an attention mechanism that allows them to focus on relevant parts of the input sequence and learn long-term dependencies in the data. This attention mechanism is what sets transformers apart from other neural network architectures like recurrent neural networks (RNNs) and convolutional neural networks (CNNs).

RNNs process input sequences one element at a time and rely on a hidden state that gets updated at each time step. However, RNNs can suffer from vanishing gradients or exploding gradients problems, which limit their ability to model long-term dependencies.

CNNs, on the other hand, are commonly used for image and speech processing and can learn local patterns in the input data by applying a series of convolutions. However, they may not be as effective as transformers when dealing with sequences of variable length.

Transformers, on the other hand, can model long-term dependencies more effectively by applying self-attention to the input sequence. This means that the model can assign different weights to different parts of the input sequence, allowing it to focus on the most relevant information. This makes them particularly well-suited for NLP tasks, where long-term dependencies are common.

In the context of PyTorch, transformers can be easily implemented and trained using pre-built packages such as Hugging Face's Transformers library, which provides a range of pre-trained transformer models for various NLP tasks. This makes it easy for researchers and practitioners to leverage the power of transformers without having to start from scratch.



Advantages of pretrained transformers in PyTorch

Pretrained transformers in PyTorch have several advantages, which have led to their widespread use in natural language processing tasks such as sentiment analysis.

  1. Transfer learning: Pretrained transformers are models that have been trained on massive amounts of data, which allows them to learn general features of language that are transferable to a wide range of downstream tasks. This makes them particularly useful for transfer learning, where a model trained on one task is fine-tuned on another related task, resulting in better performance with fewer data.
  2. Reduced training time: Since pretrained transformers have already learned a large amount of information about language, fine-tuning them on a new task requires less training time and fewer training examples. This can lead to significant time and cost savings in the model development process.
  3. Better performance: Pretrained transformers have achieved state-of-the-art performance on a wide range of natural language processing tasks, including sentiment analysis, text classification, question answering, and machine translation. This makes them a powerful tool for researchers and practitioners who want to achieve the best possible performance on these tasks.
  4. Flexibility: Pretrained transformers are available in a variety of architectures and sizes, making them flexible and adaptable to different use cases. They can be used as feature extractors, fine-tuned on specific tasks, or combined with other models to create powerful ensemble models.

Now that we have an idea about pretrained  transformers using Pytorch. Let us build a simple Sentiment Analysis model with PyTorch.  We will learn how to use Huggingface's Transformers library to rapidly and effectively execute sentiment analysis. We will be using pre-trained transformers rather than fine-tuning our own, thus we'll require a low setup cost..

Steps involved:

  • Step 1: Install Library
  • Step 2: Import Library
  • Step 3: Build Sentiment Analysis Pipeline
  • Step 4: Input Text
  • Step 5: Perform Semantic Analysis

Step 1: Install Library

!pip install transformers

Installing the transformers library is the first step in implementing the sentiment analysis pipeline using pre-trained transformers. This library provides a collection of state-of-the-art pre-trained models for natural language processing tasks, including sentiment analysis.

Step 2: Import Library

from transformers import pipeline

The !pip install transformers command is used to install the Transformers library in Python. This library is developed by Hugging Face and provides state-of-the-art implementations of various transformer models such as BERT, GPT-2, etc., and tools for natural language processing tasks such as tokenization, text classification, and language generation. This command will download and install the Transformers library in our Python environment, allowing us to use it in your code.

Step 3: Build Sentiment Analysis Pipeline

sentiment_analysis1 = pipeline("sentiment-analysis")

This will generate a pipeline that is appropriate for the sentiment analysis task. First, however, we may wonder what model and tokenizer are employed here. The Transformers library, by default, employs a DistilBERT model that was fine-tuned on the Stanford Sentiment Treebank v2 (SST2) task from the GLUE Dataset.

However, when we instantiate the pipeline, we can use a different model or tokenizer by passing them as model and tokenizer parameters.

Step 4: Input Text

positive_text = "I enjoy playing"
negative_text = "I dislike late night parties."

We will use these two text samples for sentiment analysis.

Step 5: Perform Semantic Analysis

result1 = sentiment_analysis1(positive_text)[0]
print("Label:", result1['label'])
print("Confidence Score:", result1['score'])
result2 = sentiment_analysis1(negative_text)[0]
print("Label:", result2['label'])
print("Confidence Score:", result2['score'])

The sentiment_analysis1() function takes an input text, tokenizes it, encodes it, and feeds it into a pre-trained transformer model. The output of the model is a score indicating the confidence level of the model's prediction and a label indicating whether the sentiment of the input text is positive or negative.

The  input text, positive_text/negative_text contains a positive/negative sentiment. The output of applying the sentiment_analysis1() function to this input text is a dictionary named result1, which contains the model's prediction label and confidence score.

The code then prints the prediction label and confidence score using the print() function. The label indicates the sentiment of the input text, either "positive" or "negative", and the confidence score indicates how certain the model is about its prediction, with a value between 0 and 1.

We could see how a sample of positive and negative text was used to showcase the model's ability to predict sentiment with high confidence scores accurately.


Using PyTorch and pretrained Transformers, Sentiment analysis is a powerful tool for analyzing and understanding human emotions and opinions from textual data. With state-of-the-art models such as BERT, it is now possible to achieve high accuracy and confidence in predicting the sentiment of a text. This technology has numerous practical applications in various fields, such as business and social media, where understanding the emotions and opinions of customers and users is critical for decision-making. With the availability of the Transformers library and pre-trained models, sentiment analysis has become more accessible and easier to implement. The future of sentiment analysis using PyTorch and Transformers looks bright. We expect to see more advancements in this area as more data becomes available and new models are developed.

If you are interested in learning more about pretrained Transformers and aim to become a Data Scientist, join AlmaBetter’s Full Stack Data Science program. They offer a 100% placement guarantee with jobs that pay Rs. 5-25 LPA. Enroll today!

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