Make python3 default Python for docs build

docs/Makefile

@@ -1,144 +1,144 b''
 # Makefile for Sphinx documentation
 #
 
 # You can set these variables from the command line.
 SPHINXOPTS    =
 SPHINXBUILD   = sphinx-build
 PAPER         =
 SRCDIR        = source
 BUILDDIR      = build
-PYTHON        = python
+PYTHON        = python3
 
 # Internal variables.
 PAPEROPT_a4     = -D latex_paper_size=a4
 PAPEROPT_letter = -D latex_paper_size=letter
 ALLSPHINXOPTS   = -d build/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) $(SRCDIR)
 
 .PHONY: help clean html web pickle htmlhelp latex changes linkcheck api
 
 default: html
 
 help:
 	@echo "Please use \`make <target>' where <target> is one of"
 	@echo "  html        standalone HTML files"
 	@echo "  html_noapi  same as above, without the time consuming API docs"
 	@echo "  pickle      pickle files (usable by e.g. sphinx-web)"
 	@echo "  htmlhelp    HTML files and a HTML help project"
 	@echo "  latex       LaTeX files, you can set PAPER=a4 or PAPER=letter"
 	@echo "  texinfo     Texinfo files"
 	@echo "  info        Texinfo files and run them through makeinfo"
 	@echo "  changes     an overview over all changed/added/deprecated items"
 	@echo "  linkcheck   check all external links for integrity (takes a long time)"
 	@echo
 	@echo "Compound utility targets:"
 	@echo "pdf          latex and then runs the PDF generation"
 	@echo "all          html and pdf"
 	@echo "dist         all, and then puts the results in dist/"
 
 clean_api:
 	-rm -rf $(SRCDIR)/api/generated
 
 clean: clean_api
 	-rm -rf build/* dist/*
 	-rm -f $(SRCDIR)/config/options/config-generated.txt
 	-rm -f $(SRCDIR)/config/shortcuts/*.csv
 	-rm -f $(SRCDIR)/interactive/magics-generated.txt
 
 pdf: latex
 	cd build/latex && make all-pdf
 
 all: html pdf
 
 # For final distribution, only build HTML (our pdf is now so large as to be
 # unusable, takes forever to build and just bloats the downloads).  We leave
 # them hardlinked at the top-level so users find them easily, though the
 # original build/html dir is left in-place (useful to reload builds while
 # testing).
 dist: html
 	rm -rf html
 	cp -al build/html .
 	@echo "Build finished.  Final docs are in html/"
 
 html: api autoconfig automagic autogen_shortcuts
 html_noapi: clean_api autoconfig automagic autogen_shortcuts
 
 html html_noapi:
 	mkdir -p build/html build/doctrees
 	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) build/html
 	@echo
 	@echo "Build finished. The HTML pages are in build/html."
 
 automagic: source/interactive/magics-generated.txt
 
 source/interactive/magics-generated.txt: autogen_magics.py
 	$(PYTHON) autogen_magics.py
 	@echo "Created docs for line & cell magics"
 
 autoconfig: source/config/options/config-generated.txt
 
 source/config/options/config-generated.txt:
 	$(PYTHON) autogen_config.py
 	@echo "Created docs for config options"
 
 api: source/api/generated/gen.txt
 
 source/api/generated/gen.txt:
 	$(PYTHON) autogen_api.py
 	@echo "Build API docs finished."
 
 autogen_shortcuts: autogen_shortcuts.py ../IPython/terminal/interactiveshell.py source/config/shortcuts/index.rst
 	$(PYTHON) autogen_shortcuts.py
 	@echo "Created docs for shortcuts"
 
 pickle:
 	mkdir -p build/pickle build/doctrees
 	$(SPHINXBUILD) -b pickle $(ALLSPHINXOPTS) build/pickle
 	@echo
 	@echo "Build finished; now you can process the pickle files or run"
 	@echo "  sphinx-web build/pickle"
 	@echo "to start the sphinx-web server."
 
 web: pickle
 
 htmlhelp:
 	mkdir -p build/htmlhelp build/doctrees
 	$(SPHINXBUILD) -b htmlhelp $(ALLSPHINXOPTS) build/htmlhelp
 	@echo
 	@echo "Build finished; now you can run HTML Help Workshop with the" \
 	      ".hhp project file in build/htmlhelp."
 
 latex: api autoconfig
 	mkdir -p build/latex build/doctrees
 	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) build/latex
 	@echo
 	@echo "Build finished; the LaTeX files are in build/latex."
 	@echo "Run \`make all-pdf' or \`make all-ps' in that directory to" \
 	      "run these through (pdf)latex."
 
 changes:
 	mkdir -p build/changes build/doctrees
 	$(SPHINXBUILD) -b changes $(ALLSPHINXOPTS) build/changes
 	@echo
 	@echo "The overview file is in build/changes."
 
 linkcheck:
 	mkdir -p build/linkcheck build/doctrees
 	$(SPHINXBUILD) -b linkcheck $(ALLSPHINXOPTS) build/linkcheck
 	@echo
 	@echo "Link check complete; look for any errors in the above output " \
 	      "or in build/linkcheck/output.rst."
 
 texinfo:
 	mkdir -p $(BUILDDIR)/texinfo
 	$(SPHINXBUILD) -b texinfo $(ALLSPHINXOPTS) $(BUILDDIR)/texinfo
 	@echo
 	@echo "Build finished. The Texinfo files are in $(BUILDDIR)/texinfo."
 	@echo "Run \`make' in that directory to run these through makeinfo" \
 	      "(use \`make info' here to do that automatically)."
 
 info:
 	mkdir -p $(BUILDDIR)/texinfo
 	$(SPHINXBUILD) -b texinfo $(ALLSPHINXOPTS) $(BUILDDIR)/texinfo
 	@echo "Running Texinfo files through makeinfo..."
 	make -C $(BUILDDIR)/texinfo info
 	@echo "makeinfo finished; the Info files are in $(BUILDDIR)/texinfo."