Question: I created the requirements.txt with pip freeze > requirements.txt. Some modules show the @file..... instead of the version #. What does it mean and why it show? Conda: 4.8.3 Here is the result of requirements.txt. e.g. astroid, flask-admin, matplotlib shows "@ file" below astroid @ file:///opt/concourse/worker/volumes/live/b22b518b-f584-4586-5ee9-55bfa4fca96e/volume/astroid_1592495912194/work bcrypt==3.1.7 blinker==1.4 certifi==2020.6.20 cffi==1.14.0 click==7.1.2 cycler==0.10.0 dnspython==1.16.0 ecdsa==0.13 email-validator @ file:///home/conda/feedstock_root/build_artifacts/email_validator_1589962946737/work flake8==3.8.3 Flask==1.1.2 Flask-Admin @ file:///tmp/build/80754af9/flask-admin_1592429635880/work Flask-Bcrypt==0.7.1 Flask-Login==0.5.0 Flask-Mail==0.9.1 flask-msearch==0.2.9 Flask-SQLAlchemy==2.4.3 Flask-WTF==0.14.3 gunicorn==20.0.4 idna==2.9 importlib-metadata==1.6.1 isort==4.3.21 itsdangerous==1.1.0 Jinja2==2.11.2 kiwisolver==1.2.0 lazy-object-proxy==1.4.3 MarkupSafe==1.1.1 matplotlib @ file:///Users/runner/miniforge3/conda-bld/matplotlib-base_1592576116805/work mccabe==0.6.1 mkl-fft==1.1.0 mkl-random==1.1.1 mkl-service==2.3.0 numpy==1.18.5 pandas @ file:///opt/concourse/worker/volumes/live/38d1301c-8fa9-4d2f-662e-34dddf33b183/volume/pandas_1592841668171/work psycopg2==2.8.4 pycodestyle @ file:///home/conda/feedstock_root/build_artifacts/pycodestyle_1589305246696/work pycparser==2.20 pycryptodome==3.9.7 pyflakes==2.2.0 pylint @ file:///opt/concourse/worker/volumes/live/42ede439-2571-4cb2-513c-394625d2381b/volume/pylint_1592496039330/work pyparsing==2.4.7 python-dateutil==2.8.1 pytz==2020.1 six @ file:///home/conda/feedstock_root/build_artifacts/six_1590081179328/work SQLAlchemy==1.3.17 toml @ file:///tmp/build/80754af9/toml_1592853716807/work tornado==6.0.4 typed-ast==1.4.1 Werkzeug==1.0.1 wrapt==1.11.2 WTForms==2.3.1 xlrd==1.2.0 zipp==3.1.0  Here is the conda list astroid 2.4.2 py37_0 anaconda bcrypt 3.1.7 py37h9bfed18_1 conda-forge blas 1.0 mkl anaconda blinker 1.4 py_1 conda-forge ca-certificates 2020.1.1 0 anaconda certifi 2020.6.20 py37_0 anaconda cffi 1.14.0 py37h356ff06_0 conda-forge click 7.1.2 py_0 anaconda cycler 0.10.0 py_2 conda-forge dnspython 1.16.0 py_1 conda-forge ecdsa 0.13 py_0 conda-forge email_validator 1.1.1 pyh9f0ad1d_0 conda-forge flake8 3.8.3 py_0 anaconda flask 1.1.2 py_0 anaconda flask-admin 1.5.4 py_0 anaconda flask-bcrypt 0.7.1 py_1 conda-forge flask-login 0.5.0 py_0 anaconda flask-mail 0.9.1 py_2 conda-forge flask-msearch 0.2.9 pypi_0 pypi flask-sqlalchemy 2.4.3 pypi_0 pypi flask-wtf 0.14.3 py_0 anaconda freetype 2.10.2 h8da9a1a_0 conda-forge gmp 6.2.0 h4a8c4bd_2 conda-forge gunicorn 20.0.4 py37_0 anaconda idna 2.9 py_1 conda-forge importlib-metadata 1.6.1 py37_0 anaconda intel-openmp 2020.1 216 anaconda isort 4.3.21 py37_0 anaconda itsdangerous 1.1.0 py37_0 anaconda jinja2 2.11.2 py_0 anaconda kiwisolver 1.2.0 py37ha1cc60f_0 conda-forge krb5 1.16.4 hddcf347_0 anaconda lazy-object-proxy 1.4.3 py37h1de35cc_0 anaconda libcxx 10.0.0 1 libedit 3.1.20191231 haf1e3a3_0 libffi 3.2.1 h0a44026_6 libgfortran 3.0.1 h93005f0_2 anaconda libpng 1.6.37 hbbe82c9_1 conda-forge libpq 11.2 h051b688_0 anaconda markupsafe 1.1.1 py37h1de35cc_0 anaconda matplotlib 3.2.2 0 conda-forge matplotlib-base 3.2.2 py37hddda452_0 conda-forge mccabe 0.6.1 py37_1 anaconda mkl 2019.4 233 anaconda mkl-service 2.3.0 py37hfbe908c_0 anaconda mkl_fft 1.1.0 py37hc64f4ea_0 anaconda mkl_random 1.1.1 py37h959d312_0 anaconda ncurses 6.2 h0a44026_1 numpy 1.18.5 py37h1da2735_0 anaconda numpy-base 1.18.5 py37h3304bdc_0 anaconda openssl 1.1.1g h1de35cc_0 anaconda pandas 1.0.5 py37h959d312_0 anaconda pip 20.1.1 py37_1 psycopg2 2.8.4 py37ha12b0ac_0 anaconda pycodestyle 2.6.0 pyh9f0ad1d_0 conda-forge pycparser 2.20 py_0 conda-forge pycryptodome 3.9.7 py37h51495b9_1 conda-forge pyflakes 2.2.0 py_0 anaconda pylint 2.5.3 py37_0 anaconda pyparsing 2.4.7 pyh9f0ad1d_0 conda-forge python 3.7.6 h359304d_2 python-dateutil 2.8.1 py_0 anaconda python_abi 3.7 1_cp37m conda-forge pytz 2020.1 py_0 anaconda readline 7.0 h1de35cc_5 setuptools 47.3.1 py37_0 six 1.15.0 pyh9f0ad1d_0 conda-forge sqlalchemy 1.3.17 pypi_0 pypi sqlite 3.32.3 hffcf06c_0 tk 8.6.10 hb0a8c7a_0 toml 0.10.1 py_0 anaconda tornado 6.0.4 py37h9bfed18_1 conda-forge typed-ast 1.4.1 py37h1de35cc_0 anaconda werkzeug 1.0.1 py_0 anaconda wheel 0.34.2 py37_0 wrapt 1.11.2 py37h1de35cc_0 anaconda wtforms 2.3.1 py_0 anaconda xlrd 1.2.0 py37_0 anaconda xz 5.2.5 h1de35cc_0 zipp 3.1.0 py_0 anaconda zlib 1.2.11 h1de35cc_3  Finally I plan to deploy app in Heroku, so I thought that requirements.txt may be required.

Answer: This is a special syntax (supported since pip 19.1) to install packages from VCS repositories : package_name @ git+https://githost/<repo>.git@<commit_id>  See https://pip.readthedocs.io/en/stable/reference/pip_install/#requirement-specifiers and https://www.python.org/dev/peps/pep-0440/#direct-references