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CVAT follows strict coding standards to maintain code quality and consistency across the project. This guide covers the style guidelines for different programming languages used in CVAT.

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General Principles

  • Write readable code: Code is read more often than written
  • Be consistent: Follow existing patterns in the codebase
  • Document your code: Add comments for complex logic
  • Keep it simple: Avoid unnecessary complexity
  • Test your changes: Ensure code works as expected

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Python Code Style

CVAT’s Python code follows PEP 8 with some modifications enforced by Black and isort.

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Formatters and Linters

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Black

Black is used for automatic code formatting with these settings: 
[tool.black]
line-length = 100
target-version = ['py310']
Format your Python code: 
black cvat/

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isort

Isort organizes imports with Black-compatible settings: 
[tool.isort]
profile = "black"
line_length = 100
forced_separate = ["tests"]
Sort imports: 
isort cvat/

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pylint

Pylint is used for static code analysis. Run it to check for issues: 
pylint cvat/

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Python Style Guidelines

  • Line length: Maximum 100 characters
  • Indentation: 4 spaces (no tabs)
  • Imports: Group imports (standard library, third-party, local) and sort alphabetically
  • Naming conventions:
    • Classes: PascalCase
    • Functions and variables: snake_case
    • Constants: UPPER_SNAKE_CASE
    • Private members: _leading_underscore

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Example

from typing import List, Optional

import django
from rest_framework import serializers

from cvat.apps.engine.models import Task


class TaskSerializer(serializers.ModelSerializer):
    """Serializer for Task model with custom validation."""

    def validate_name(self, value: str) -> str:
        """Validate that task name is not empty."""
        if not value.strip():
            raise serializers.ValidationError("Task name cannot be empty")
        return value

    class Meta:
        model = Task
        fields = "__all__"

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JavaScript/TypeScript Code Style

The frontend uses ESLint and Prettier for code quality and formatting.

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ESLint Configuration

CVAT uses a strict ESLint configuration based on Airbnb style guide: 
// Key rules
{
  "indent": ["error", 4],
  "max-len": ["error", { "code": 120 }],
  "quotes": ["error", "single"],
  "semi": ["error", "always"]
}

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Prettier Configuration

Prettier enforces consistent formatting: 
{
  "printWidth": 120,
  "tabWidth": 4,
  "singleQuote": true,
  "semi": true,
  "trailingComma": "all",
  "arrowParens": "always",
  "jsxSingleQuote": true
}

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Running Linters

Check code style: 
# ESLint
yarn run lint

# Prettier
yarn run prettier --check .
Auto-fix issues: 
# ESLint
yarn run lint --fix

# Prettier
yarn run prettier --write .

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TypeScript/JavaScript Style Guidelines

  • Line length: Maximum 120 characters
  • Indentation: 4 spaces
  • Quotes: Single quotes for strings, JSX props use single quotes
  • Semicolons: Always required
  • Naming conventions:
    • Interfaces/Types: PascalCase
    • Functions/Variables: camelCase
    • Constants: UPPER_SNAKE_CASE
    • React components: PascalCase
    • Private members: _leadingUnderscore

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TypeScript Example

import React from 'react';
import { Task } from 'cvat-core-wrapper';

interface TaskItemProps {
    task: Task;
    onSelect: (taskId: number) => void;
}

export default function TaskItem({ task, onSelect }: TaskItemProps): JSX.Element {
    const handleClick = (): void => {
        onSelect(task.id);
    };

    return (
        <div className='task-item' onClick={handleClick}>
            <h3>{task.name}</h3>
            <p>{task.status}</p>
        </div>
    );
}

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File Organization

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Python Files

# Copyright header
# SPDX-License-Identifier: MIT

"""Module docstring describing the file purpose."""

# Standard library imports
import os
import sys

# Third-party imports
import django
from rest_framework import viewsets

# Local imports
from cvat.apps.engine.models import Task

# Constants
MAX_RETRY_COUNT = 3

# Module code

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TypeScript/JavaScript Files

// Copyright (C) CVAT.ai Corporation
// SPDX-License-Identifier: MIT

// External imports
import React from 'react';
import { useSelector } from 'react-redux';

// CVAT imports
import { Task } from 'cvat-core-wrapper';

// Local imports
import './styles.scss';

// Constants
const MAX_ITEMS_PER_PAGE = 10;

// Component code

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Comments and Documentation

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Python Docstrings

Use Google-style docstrings: 
def create_task(name: str, owner_id: int, labels: List[str]) -> Task:
    """Create a new annotation task.

    Args:
        name: The task name
        owner_id: ID of the task owner
        labels: List of label names

    Returns:
        The created Task instance

    Raises:
        ValidationError: If task name is invalid
    """
    pass

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TypeScript/JSDoc Comments

/**
 * Calculate the annotation completion percentage
 * @param completed - Number of completed frames
 * @param total - Total number of frames
 * @returns Percentage value between 0 and 100
 */
function calculateProgress(completed: number, total: number): number {
    return (completed / total) * 100;
}

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Git Commit Messages

Write clear, descriptive commit messages: 
Short summary (50 chars or less)

Detailed explanation of the changes if needed. Wrap at 72 characters.
Explain the problem this commit solves and why this approach was chosen.

- Use bullet points for multiple changes
- Reference issues: Fixes #123, Resolves #456
- Break lines at 72 characters
Good commit message examples:
  • Fix annotation export for rotated bounding boxes
  • Add support for video chapters in frame navigation
  • Refactor task creation to improve performance
  • Update dependencies to fix security vulnerabilities

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Pre-commit Hooks

CVAT uses linters in CI/CD. Before committing, run: 
# Python
black cvat/
isort cvat/
pylint cvat/

# JavaScript/TypeScript
yarn run lint --fix
yarn run prettier --write .

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Code Review Guidelines

When reviewing code:
  • Check for adherence to style guidelines
  • Verify tests are included and passing
  • Look for potential bugs or edge cases
  • Ensure code is readable and maintainable
  • Provide constructive feedback
  • Approve when requirements are met

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Security Considerations

ESLint includes security plugins: 
plugins: ['security', 'no-unsanitized']
Always:
  • Sanitize user input
  • Avoid eval() and similar dangerous functions
  • Use parameterized queries for database access
  • Validate and escape data before rendering

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Editor Configuration

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VS Code

Recommended extensions:
  • Python (Microsoft)
  • Pylance
  • ESLint
  • Prettier
  • EditorConfig
Settings: 
{
  "editor.formatOnSave": true,
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": true
  },
  "python.formatting.provider": "black",
  "python.linting.pylintEnabled": true
}

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PyCharm/WebStorm

Configure:
  • Black as the Python formatter
  • ESLint for JavaScript/TypeScript
  • Prettier for auto-formatting
  • Line length to 100 (Python) or 120 (JS/TS)

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Continuous Integration

CVAT’s CI runs these checks on every pull request:
  • Linters: ESLint, Pylint, Black, isort
  • Type checking: TypeScript compiler, mypy
  • Security: CodeQL analysis
  • Tests: Unit, integration, and E2E tests
Ensure your code passes all checks before submitting a PR.

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