Installing Flask web server...
Looking in indexes: https://pypi.org/simple, https://www.piwheels.org/simple
Collecting flask
Downloading https://files.pythonhosted.org/packages/f2/28/2a03252dfb9ebf377f40fba6a7841b47083260bf8bd8e737b0c6952df83f/Flask-1.1.2-py2.py3-none-any.whl (94kB)
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Collecting click>=5.1 (from flask)
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Collecting Werkzeug>=0.15 (from flask)
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Collecting cffi!=1.11.3,>=1.8 (from cryptography>=2.8->pyopenssl)
Downloading https://files.pythonhosted.org/packages/f7/09/88bbe20b76ca76be052c366fe77aa5e3cd6e5f932766e5597fecdd95b2a8/cffi-1.14.2.tar.gz (470kB)
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Collecting pycparser (from cffi!=1.11.3,>=1.8->cryptography>=2.8->pyopenssl)
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Building wheels for collected packages: cffi
Running setup.py bdist_wheel for cffi ... error
Complete output from command /usr/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-2syp6qys/cffi/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" bdist_wheel -d /tmp/pip-wheel-7kz29q_q --python-tag cp37:
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containing `libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containing `libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containing `libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containing `libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
Package libffi was not found in the pkg-config search path.
Perhaps you should add the directory containing `libffi.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libffi' found
running bdist_wheel
running build
running build_py
creating build
creating build/lib.linux-armv6l-3.7
creating build/lib.linux-armv6l-3.7/cffi
copying cffi/pkgconfig.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/vengine_gen.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/ffiplatform.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/verifier.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/backend_ctypes.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/vengine_cpy.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/__init__.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/commontypes.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/lock.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/cparser.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/setuptools_ext.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/recompiler.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/model.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/error.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/cffi_opcode.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/api.py -> build/lib.linux-armv6l-3.7/cffi
copying cffi/_cffi_include.h -> build/lib.linux-armv6l-3.7/cffi
copying cffi/parse_c_type.h -> build/lib.linux-armv6l-3.7/cffi
copying cffi/_embedding.h -> build/lib.linux-armv6l-3.7/cffi
copying cffi/_cffi_errors.h -> build/lib.linux-armv6l-3.7/cffi
running build_ext
building '_cffi_backend' extension
creating build/temp.linux-armv6l-3.7
creating build/temp.linux-armv6l-3.7/c
arm-linux-gnueabihf-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -DUSE__THREAD -DHAVE_SYNC_SYNCHRONIZE -I/usr/include/ffi -I/usr/include/libffi -I/usr/include/python3.7m -c c/_cffi_backend.c -o build/temp.linux-armv6l-3.7/c/_cffi_backend.o
c/_cffi_backend.c:15:10: fatal error: ffi.h: No such file or directory
#include <ffi.h>
^~~~~~~
compilation terminated.
error: command 'arm-linux-gnueabihf-gcc' failed with exit status 1
----------------------------------------
Failed building wheel for cffi
Running setup.py clean for cffi
