RF: use sys.executable not hardcoded "python"

this would allow to consistently use the same python (which might be
python3 with python corresponding to python v 2)

Author: yarikoptic

doc/conf.py

@@ -16,6 +16,7 @@
 from pathlib import Path
 from tempfile import TemporaryDirectory
 import shutil
+import sys
 from packaging.version import Version
 import nipype
 import subprocess as sp
@@ -54,7 +55,7 @@
 
 sp.run(
     [
-        "python",
+        sys.executable,
         ex2rst,
         "--outdir",
         str(example_dir),
@@ -70,7 +71,7 @@
 )
 sp.run(
     [
-        "python",
+        sys.executable,
         ex2rst,
         "--outdir",
         str(example_dir),

tools/toollib.py

@@ -31,7 +31,7 @@ def sh(cmd):
 def compile_tree():
     """Compile all Python files below current directory."""
     vstr = ".".join(map(str, sys.version_info[:2]))
-    stat = os.system("python %s/lib/python%s/compileall.py ." % (sys.prefix, vstr))
+    stat = os.system("%s %s/lib/python%s/compileall.py ." % (sys.executable, sys.prefix, vstr))
     if stat:
         msg = "*** ERROR: Some Python files in tree do NOT compile! ***\n"
         msg += "See messages above for the actual file that produced it.\n"