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requirements.txt

Learn dependency management with requirements.txt.

requirements.txt

requirements.txt lists the dependencies of a project, one per line. The pip install -r requirements.txt command installs every package in the list. It is used as an alternative to pyproject.toml in production deployments.

requests>=2.28
httpx==0.24

Each line holds a package and an optional version specifier. The pip freeze > requirements.txt command produces this file by freezing the exact versions of installed packages.

Version specifiers

Dependency lines use version specifiers: >= means at least, == means exact, < means less than, ~= means compatible release.

requests>=2.28    # at least 2.28
httpx==0.24      # exactly 0.24
rich<13         # less than 13

In production, locking with == gives predictability. In development, >= is more flexible but may surprise you on major version bumps.

Practice Count the lines in requirements.txt

Assign the following content to a string variable named requirements:

requests>=2.28
httpx==0.24

Then list the lines with deps = [line for line in requirements.strip().split("\n") if line.strip()]. Print the line count with print(len(deps)) and the first line with print(deps[0]).

Starter code

main.py
# assign a two-line dependency list to a string named requirements
# turn the lines into a list, dropping blank lines
# print the line count and the first line

Sample solution

main.py
requirements = "requests>=2.28\nhttpx==0.24\n"

deps = [line for line in requirements.strip().split("\n") if line.strip()]
print(len(deps))
print(deps[0])

Expected output

2
requests>=2.28

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does pip freeze > requirements.txt do?

  • Builds a wheel
  • Removes packages
  • Creates a virtual environment
  • Freezes installed versions Correct answer

Explanation: pip freeze writes the exact versions of installed packages to the file.

2 Complete the >= specifier

Question 
requests____2.28
Answer 
requests>=2.28

Explanation: >= requires at least this version.

3 Match the version specifiers

Term Meaning
>= At least
== Exact
< Less than
~= Compatible

All lessons in Advanced

1 Advanced decorators

  1. Parameterized decorator
  2. Class decorator
  3. functools
  4. functools.partial
  5. functools.reduce
  6. Summary - Advanced decorators

2 Type hints

  1. Basic hints
  2. Optional and Union
  3. typing.List and Dict
  4. Callable
  5. TypeVar
  6. Summary - Type hints

3 Pytest

  1. pytest basics
  2. assert
  3. fixture
  4. parametrize
  5. monkeypatch
  6. Summary - Pytest

4 Mocking

  1. unittest.mock
  2. patch
  3. MagicMock
  4. side_effect
  5. assert_called
  6. Summary - Mocking

5 Async basics

  1. async/await
  2. asyncio.run
  3. async def
  4. await asyncio.sleep
  5. create_task
  6. Summary - Async basics

6 Asyncio

  1. gather
  2. wait
  3. Queue
  4. Lock
  5. Semaphore
  6. Summary - Asyncio

7 HTTP and aiohttp

  1. urllib
  2. aiohttp.ClientSession
  3. async get
  4. async post
  5. JSON response
  6. Summary - HTTP and aiohttp

8 SQLAlchemy

  1. Engine
  2. Session
  3. Defining models
  4. Column and type
  5. Query
  6. Summary - SQLAlchemy

9 FastAPI

  1. FastAPI app
  2. @app.get
  3. Pydantic model
  4. Path parameter
  5. Query parameter
  6. Summary - FastAPI

10 Pydantic

  1. BaseModel
  2. Field
  3. validator
  4. Config
  5. parse_obj
  6. Summary - Pydantic

11 Design patterns

  1. Singleton
  2. Factory
  3. Strategy
  4. Observer
  5. Decorator
  6. Summary - Design patterns

12 Logging

  1. logging.getLogger
  2. Log levels
  3. basicConfig
  4. FileHandler
  5. dictConfig
  6. Summary - Logging

13 Packaging

  1. pyproject.toml
  2. setuptools
  3. Virtual environment
  4. pip install
  5. requirements.txt
  6. Summary - Packaging

14 Advanced final

  1. Project design
  2. Async layer
  3. SQLAlchemy layer
  4. FastAPI layer
  5. Putting it together