use python3 only for building

Python 2 is very near end-of-life, and Python3-compatible changes to a
few scripts introduced compatibility problems with 2.7 again.  It went
unnoticed for me since my system symlinks "python" to "python3", but
it broke the build on systems where that symlink is still python2.  At
this point in time, I feel it is worth targetting modern Python and
forgetting about 2.7.

COMPILING.adoc

@@ -17,8 +17,8 @@ Building the Freedoom IWADs pretty much simply requires the following:
     portability are most welcome!).  On non-GNU systems, it might be
     available in a package and binary named as _gmake_.
   * _Python_: Freedoom uses several Python programs in its tree to
-    assist with building the IWADs.  Both Python 2.7 and 3.x are fully
-    supported.
+    assist with building the IWADs.  Python 3.x is required, we no
+    longer support Python 2.
   * _Pillow_: A Python image manipulation module that provides the
     features we need for scaling and composing various graphics of the
     game.

bootstrap/bootstrap

@@ -1,6 +1,5 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
-from __future__ import print_function
 import sys
 import struct
 

dist/pillow-compose

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Simple and dumb Pillow-based compositor
 # Usage: pillow-compose src-img.png dst-img.png WIDTH HEIGHT

dist/pillow-resize

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # Simple and dumb Pillow-based resizer
 # Usage: pillow-resize src-img.png dst-img.png WIDTH HEIGHT

graphics/text/create_caption

@@ -1,8 +1,7 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # encoding: utf-8
 # SPDX-License-Identifier: BSD-3-Clause
 
-from __future__ import unicode_literals
 from PIL import Image, ImageFont, ImageDraw
 import sys
 import os

graphics/text/image_dimensions.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 import re

graphics/text/rotate

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # SPDX-License-Identifier: BSD-3-Clause
 

graphics/text/smtextgen

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Script to generate text graphics using the "small" (HUD) font.

graphics/text/textgen

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Script to generate menu and intermission screen 'text' graphics for

graphics/text/tint.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 # SPDX-License-Identifier: MIT
 # Copyright (c) 2017 Martin Miller, Nick Zatkovich

lumps/colormap/colormap

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Copyright (C) 2001 Colin Phipps <cphipps@doomworld.com>
 # Copyright (C) 2008, 2013 Simon Howard
 # Parts copyright (C) 1999 by id Software (http://www.idsoftware.com/)

lumps/dmxgus/gather_stats.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Script to gather statistics from MIDI files about instrument usage.

lumps/dmxgus/gen-ultramid

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Config file generator for the DMXGUS lump / config file.

lumps/genmidi/README.adoc

@@ -121,7 +121,7 @@ to specify a note you want to play. For example, for 'C#' in Octave -3:
 Once you're done, save your changes and type this to build a new GENMIDI
 for testing:
 
-  python mkgenmidi genmidi.lmp
+  python3 mkgenmidi genmidi.lmp
 
 To try it out, get a source port with OPL emulation support (eg. Chocolate
 Doom) and add genmidi.lmp on the command line, eg.
@@ -137,8 +137,7 @@ editors instead of AT2. There's a useful script included that will do
 exactly this. Specify the name of the a2i file and the name of the
 desired output file, as follows:
 
-  python a2i-to-sbi snazzy.a2i snazzy.sbi
+  python3 a2i-to-sbi snazzy.a2i snazzy.sbi
 
 Don't forget to update config.py to use the .sbi version of the file
 instead of the .a2i version!
-

lumps/genmidi/a2i-to-sbi

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 import a2i_file

lumps/genmidi/a2i_file.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Module to load A2I (AdlibTracker 2) instrument files.

lumps/genmidi/config.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Config file for GENMIDI file generation.

lumps/genmidi/dumpgenmidi

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Dump the contents of a GENMIDI lump into separate .sbi instrument files,

lumps/genmidi/genmidi.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Module for interacting with Doom GENMIDI lumps.

lumps/genmidi/instrument.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Module to load OPL instrument files.

lumps/genmidi/midi.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Constants for MIDI notes.

lumps/genmidi/mkgenmidi

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 import genmidi

lumps/genmidi/sbi_file.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Module to load Creative SBI OPL instrument files.

lumps/playpal/playpal

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # Script to generate the PLAYPAL lump used by the Doom engine, specifically the
 # which contains 14 alternative palettes which are used for various
 # environmental effects. The base palette from which these are derived is either

lumps/textures/build-textures

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Texture lump builder for Freedoom

scripts/fix-gfx-offsets

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 from os import path

scripts/fix-map-names

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # fix-map-names - Fix map names in WAD files
@@ -10,8 +10,6 @@
 # or make target "test-map-names" ("-t" option). Make target "test"
 # ("-t" option) will run this and any other test.
 
-from __future__ import print_function
-
 # Imports
 
 import argparse

scripts/makejson

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 import hashlib

scripts/makepkgs

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 
 import os

scripts/music-duplicates

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # Find duplicated music tracks and create a summary report of music

scripts/simplecpp

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # SPDX-License-Identifier: BSD-3-Clause
 #
 # simple cpp-style preprocessor