Question: OS: Windows 10 Python ver: 3.9.0 Error code: ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.  I tried: python -m pip install -U pip python -m pip install -U matplotlib  didn't work. and then I tried: pip install --upgrade setuptools  didn't solve the problem. I read on SO that maybe if I open the shell in administrator mode it could solve the problem but it didn't work too. I saw someone mentioning ez-setup for this error code. I installed it but that didn't work too. I don't know if it has something to do but my C directory looks like this: C:\Users\METİNUSTA  It has an uppercase i character which sometimes can cause problems with applications. I can't change it because I am using my school's Windows key and it don't let me do any change. Because of this I installed python on D: . Also here my pip list for extra information: ez-setup 0.9 flake8 3.8.4 mccabe 0.6.1 pip 20.2.4 pycodestyle 2.6.0 pyflakes 2.2.0 setuptools 50.3.2 wheel 0.35.1  and finally whole error log that I get on windows powershell:  ERROR: Command errored out with exit status 1: command: 'd:\python\python39\python.exe' -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'C:\\Users\\METİNUSTA\\AppData\\Local\\Temp\\pip-install-8iv10tb_\\matplotlib\\setup.py'"'"'; __file__='"'"'C:\\Users\\METİNUSTA\\AppData\\Local\\Temp\\pip-install-8iv10tb_\\matplotlib\\setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base 'C:\Users\METİNUSTA\AppData\Local\Temp\pip-pip-egg-info-elosrn6m' cwd: C:\Users\METİNUSTA\AppData\Local\Temp\pip-install-8iv10tb_\matplotlib\ Complete output (99 lines): WARNING: Missing build requirements in pyproject.toml for numpy>=1.15 from https://files.pythonhosted.org/packages/bf/e8/15aea783ea72e2d4e51e3ec365e8dc4a1a32c9e5eb3a6d695b0d58e67cdd/numpy-1.19.2.zip#sha256=0d310730e1e793527065ad7dde736197b705d0e4c9999775f212b03c44a8484c. WARNING: The project does not specify a build backend, and pip cannot fall back to setuptools without 'setuptools>=40.8.0' and 'wheel'. ERROR: Command errored out with exit status 1: command: 'd:\python\python39\python.exe' 'd:\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py' prepare_metadata_for_build_wheel 'C:\Users\METNUS~1\AppData\Local\Temp\tmpqz3brme_' cwd: C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy Complete output (49 lines): Error in sitecustomize; set PYTHONVERBOSE for traceback: SyntaxError: (unicode error) 'utf-8' codec can't decode byte 0xdd in position 0: unexpected end of data (sitecustomize.py, line 21) Running from numpy source directory. setup.py:470: UserWarning: Unrecognized setuptools command, proceeding with generating Cython sources and expanding templates run_build = parse_setuppy_commands() Error in sitecustomize; set PYTHONVERBOSE for traceback: SyntaxError: (unicode error) 'utf-8' codec can't decode byte 0xdd in position 0: unexpected end of data (sitecustomize.py, line 21) Processing numpy/random\_bounded_integers.pxd.in Processing numpy/random\bit_generator.pyx Traceback (most recent call last): File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 59, in process_pyx from Cython.Compiler.Version import version as cython_version ModuleNotFoundError: No module named 'Cython' During handling of the above exception, another exception occurred: Traceback (most recent call last): File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 235, in <module> main() File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 231, in main find_process_files(root_dir) File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 222, in find_process_files process(root_dir, fromfile, tofile, function, hash_db) File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 188, in process processor_function(fromfile, tofile) File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-wheel-l2wpf1i8\numpy\tools\cythonize.py", line 64, in process_pyx raise OSError('Cython needs to be installed in Python as a module') OSError: Cython needs to be installed in Python as a module Cythonizing sources Traceback (most recent call last): File "d:\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 280, in <module> main() File "d:\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 263, in main json_out['return_val'] = hook(**hook_input['kwargs']) File "d:\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py", line 133, in prepare_metadata_for_build_wheel return hook(metadata_directory, config_settings) File "d:\python\python39\lib\site-packages\setuptools\build_meta.py", line 161, in prepare_metadata_for_build_wheel self.run_setup() File "d:\python\python39\lib\site-packages\setuptools\build_meta.py", line 253, in run_setup super(_BuildMetaLegacyBackend, File "d:\python\python39\lib\site-packages\setuptools\build_meta.py", line 145, in run_setup exec(compile(code, __file__, 'exec'), locals()) File "setup.py", line 499, in <module> setup_package() File "setup.py", line 479, in setup_package generate_cython() File "setup.py", line 274, in generate_cython raise RuntimeError("Running cythonize failed!") RuntimeError: Running cythonize failed! ---------------------------------------- ERROR: Command errored out with exit status 1: 'd:\python\python39\python.exe' 'd:\python\python39\lib\site-packages\pip\_vendor\pep517\_in_process.py' prepare_metadata_for_build_wheel 'C:\Users\METNUS~1\AppData\Local\Temp\tmpqz3brme_' Check the logs for full command output. Traceback (most recent call last): File "d:\python\python39\lib\site-packages\setuptools\installer.py", line 126, in fetch_build_egg subprocess.check_call(cmd) File "d:\python\python39\lib\subprocess.py", line 373, in check_call raise CalledProcessError(retcode, cmd) subprocess.CalledProcessError: Command '['d:\\python\\python39\\python.exe', '-m', 'pip', '--disable-pip-version-check', 'wheel', '--no-deps', '-w', 'C:\\Users\\METNUS~1\\AppData\\Local\\Temp\\tmppoh8r2c9', '--quiet', 'numpy>=1.15']' returned non-zero exit status 1. The above exception was the direct cause of the following exception: Traceback (most recent call last): File "<string>", line 1, in <module> File "C:\Users\METİNUSTA\AppData\Local\Temp\pip-install-8iv10tb_\matplotlib\setup.py", line 242, in <module> setup( # Finally, pass this all along to distutils to do the heavy lifting. File "d:\python\python39\lib\site-packages\setuptools\__init__.py", line 152, in setup _install_setup_requires(attrs) File "d:\python\python39\lib\site-packages\setuptools\__init__.py", line 147, in _install_setup_requires dist.fetch_build_eggs(dist.setup_requires) File "d:\python\python39\lib\site-packages\setuptools\dist.py", line 673, in fetch_build_eggs resolved_dists = pkg_resources.working_set.resolve( File "d:\python\python39\lib\site-packages\pkg_resources\__init__.py", line 764, in resolve dist = best[req.key] = env.best_match( File "d:\python\python39\lib\site-packages\pkg_resources\__init__.py", line 1049, in best_match return self.obtain(req, installer) File "d:\python\python39\lib\site-packages\pkg_resources\__init__.py", line 1061, in obtain return installer(requirement) File "d:\python\python39\lib\site-packages\setuptools\dist.py", line 732, in fetch_build_egg return fetch_build_egg(self, req) File "d:\python\python39\lib\site-packages\setuptools\installer.py", line 128, in fetch_build_egg raise DistutilsError(str(e)) from e distutils.errors.DistutilsError: Command '['d:\\python\\python39\\python.exe', '-m', 'pip', '--disable-pip-version-check', 'wheel', '--no-deps', '-w', 'C:\\Users\\METNUS~1\\AppData\\Local\\Temp\\tmppoh8r2c9', '--quiet', 'numpy>=1.15']' returned non-zero exit status 1. Edit setup.cfg to change the build options; suppress output with --quiet. BUILDING MATPLOTLIB matplotlib: yes [3.3.2] python: yes [3.9.0 (tags/v3.9.0:9cf6752, Oct 5 2020, 15:34:40) [MSC v.1927 64 bit (AMD64)]] platform: yes [win32] sample_data: yes [installing] tests: no [skipping due to configuration] macosx: no [Mac OS-X only] ---------------------------------------- ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output. 

Answer: edit: matplotlib has now released wheels for python 3.9 so pip install --upgrade matplotlib should work. original answer matplotlib hasn't made a wheel yet for version 3.9 so your python attempted to build it from source. You should downgrade to python 3.8 and then everything should work