vim-patch:8.0.0251: not easy to select Python 2 or 3 (#9173)

Problem: It is not so easy to write a script that works with both Python 2 and Python 3, even when the Python code works with both.
Solution: Add 'pyxversion', :pyx, etc. (Marc Weber, Ken Takata)

https://github.com/vim/vim/commit/f42dd3c3901ea0ba38e67a616aea9953cae81b8d

6 files changed, 96 insertions, 1 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index e9579d5c86..7b463aa6ca 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2209,6 +2209,7 @@ printf({fmt}, {expr1}...)	String	format text
 pumvisible()			Number	whether popup menu is visible
 pyeval({expr})			any	evaluate |Python| expression
 py3eval({expr})			any	evaluate |python3| expression
+pyxeval({expr})			any	evaluate |python_x| expression
 range({expr} [, {max} [, {stride}]])
 				List	items from {expr} to {max}
 readfile({fname} [, {binary} [, {max}]])
@@ -6146,6 +6147,12 @@ pyeval({expr})						*pyeval()*
 		non-string keys result in error.
 		{only available when compiled with the |+python| feature}
 
+pyxeval({expr})						*pyxeval()*
+		Evaluate Python expression {expr} and return its result
+		converted to Vim data structures.
+		Uses Python 2 or 3, see |python_x| and 'pyxversion'.
+		See also: |pyeval()|, |py3eval()|
+
 							*E726* *E727*
 range({expr} [, {max} [, {stride}]])				*range()*
 		Returns a |List| with Numbers:
@@ -8517,6 +8524,7 @@ printer			Compiled with |:hardcopy| support.
 profile			Compiled with |:profile| support.
 python			Legacy Vim Python 2.x API is available. |has-python|
 python3			Legacy Vim Python 3.x API is available. |has-python|
+pythonx			Compiled with |python_x| interface. |has-pythonx|
 quickfix		Compiled with |quickfix| support.
 reltime			Compiled with |reltime()| support.
 rightleft		Compiled with 'rightleft' support.
diff --git a/runtime/doc/if_pyth.txt b/runtime/doc/if_pyth.txt
index 2da2e5147b..df4b54ef76 100644
--- a/runtime/doc/if_pyth.txt
+++ b/runtime/doc/if_pyth.txt
@@ -692,6 +692,7 @@ vim.Function object				*python-Function*
 
 To facilitate bi-directional interface, you can use |pyeval()| and |py3eval()| 
 functions to evaluate Python expressions and pass their values to Vim script.
+|pyxeval()| is also available.
 
 ==============================================================================
 9. Python 3						*python3*
@@ -723,4 +724,57 @@ You can test what Python version is available with: >
 	endif
 
 ==============================================================================
+10. Python X						*python_x* *pythonx*
+
+Because most python code can be written so that it works with Python 2.6+ and
+Python 3, the pyx* functions and commands have been written.  They work the
+same as the Python 2 and 3 variants, but select the Python version using the
+'pyxversion' setting.
+
+Set 'pyxversion' in your |vimrc| to prefer Python 2 or Python 3 for Python
+commands. Changing this setting at runtime risks losing the state of plugins
+(such as initialization).
+
+If you want to use a module, you can put it in the {rtp}/pythonx directory.
+See |pythonx-directory|.
+
+							*:pyx* *:pythonx*
+`:pyx` and `:pythonx` work similar to `:python`.  To check if `:pyx` works: >
+	:pyx print("Hello")
+
+To see what version of Python is being used: >
+	:pyx import sys
+	:pyx print(sys.version)
+<
+					*:pyxfile* *python_x-special-comments*
+`:pyxfile` works similar to `:pyfile`.  But you can add a "shebang" comment to
+force Vim to use `:pyfile` or `:py3file`: >
+  #!/any string/python2		" Shebang. Must be the first line of the file.
+  #!/any string/python3		" Shebang. Must be the first line of the file.
+  # requires python 2.x		" Maximum lines depend on 'modelines'.
+  # requires python 3.x		" Maximum lines depend on 'modelines'.
+Unlike normal modelines, the bottom of the file is not checked.
+If none of them are found, the 'pyxversion' option is used.
+							*W20* *W21*
+If Vim does not support the selected Python version a silent message will be
+printed.  Use `:messages` to read them.
+
+							*:pyxdo*
+`:pyxdo` works similar to `:pydo`.
+
+							*has-pythonx*
+To check if pyx* functions and commands are available: >
+	if has('pythonx')
+	  echo 'pyx* commands are available. (Python ' . &pyx . ')'
+	endif
+
+If you prefer Python 2 and want to fallback to Python 3, set 'pyxversion'
+explicitly in your |.vimrc|.  Example: >
+	if has('python')
+	  set pyx=2
+	elseif has('python3')
+	  set pyx=3
+	endif
+
+==============================================================================
  vim:tw=78:ts=8:noet:ft=help:norl:
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 7024a57333..63ded3152f 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1418,6 +1418,10 @@ tag	      command	      action ~
 |:python|	:py[thon]	execute Python command
 |:pydo|		:pyd[o]		execute Python command for each line
 |:pyfile|	:pyf[ile]	execute Python script file
+|:pyx|		:pyx		execute |python_x| command
+|:pythonx|	:pythonx	same as :pyx
+|:pyxdo|	:pyxd[o]	execute |python_x| command for each line
+|:pyxfile|	:pyxf[ile]	execute |python_x| script file
 |:quit|		:q[uit]		quit current window (when one window quit Vim)
 |:quitall|	:quita[ll]	quit Vim
 |:qall|		:qa[ll]		quit Vim
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 534b2025cd..bcefa1f56b 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -4471,6 +4471,30 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Insert mode completion.  When zero as much space as available is used.
 	|ins-completion-menu|.
 
+						*'pyxversion'* *'pyx'*
+'pyxversion' 'pyx'	number	(default depends on the build)
+			global
+	Specifies the python version used for pyx* functions and commands
+	|python_x|.  The default value is as follows:
+
+		|provider| installed	    Default ~
+		|+python| and |+python3|	0
+		only |+python|			2
+		only |+python3|			3
+
+	Available values are 0, 2 and 3.
+	If 'pyxversion' is 0, it is set to 2 or 3 after the first execution of
+	any python2/3 commands or functions.  E.g. `:py` sets to 2, and `:py3`
+	sets to 3. `:pyx` sets it to 3 if Python 3 is available, otherwise sets
+	to 2 if Python 2 is available.
+	See also: |has-pythonx|
+
+	If only |+python| or |+python3| are available,
+	'pyxversion' has no effect. The pyx* functions and commands are
+	always the same as the installed version.
+
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 						*'quoteescape'* *'qe'*
 'quoteescape' 'qe'	string	(default "\")
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index cf0efd7a75..98a5244345 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -813,6 +813,7 @@ Short explanation of each option:		*option-list*
 'pumwidth'	  'pw'	    minimum width of the popup menu
 'pythondll'		    name of the Python 2 dynamic library
 'pythonthreedll'	    name of the Python 3 dynamic library
+'pyxversion'	  'pyx'	    Python version used for pyx* commands
 'quoteescape'	  'qe'	    escape characters used in a string
 'readonly'	  'ro'	    disallow writing the buffer
 'redrawtime'	  'rdt'     timeout for 'hlsearch' and |:match| highlighting
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index 1742c64c3e..2e9f4723dd 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -905,7 +905,7 @@ if has("folding")
   call append("$", "foldmarker\tmarkers used when 'foldmethod' is \"marker\"")
   call append("$", "\t(local to window)")
   call <SID>OptionL("fmr")
-  call append("$", "foldnestmax\tmaximum fold depth for when 'foldmethod is \"indent\" or \"syntax\"")
+  call append("$", "foldnestmax\tmaximum fold depth for when 'foldmethod' is \"indent\" or \"syntax\"")
   call append("$", "\t(local to window)")
   call <SID>OptionL("fdn")
 endif
@@ -1295,6 +1295,10 @@ if exists("&mzschemedll")
   call append("$", "mzschemegcdll\tname of the Tcl GC dynamic library")
   call <SID>OptionG("mzschemegcdll", &mzschemegcdll)
 endif
+if has('pythonx')
+  call append("$", "pyxversion\twhether to use Python 2 or 3")
+  call append("$", " \tset pyx=" . &wd)
+endif
 
 " Install autocommands to enable mappings in option-window
 noremap <silent> <buffer> <CR> <C-\><C-N>:call <SID>CR()<CR>