diff --git a/pkgs/development/interpreters/python/cpython/3.3/default.nix b/pkgs/development/interpreters/python/cpython/3.3/default.nix
index 3ab0de96704..c561a1ed750 100644
--- a/pkgs/development/interpreters/python/cpython/3.3/default.nix
+++ b/pkgs/development/interpreters/python/cpython/3.3/default.nix
@@ -50,7 +50,17 @@ in stdenv.mkDerivation {
 
   NIX_LDFLAGS = stdenv.lib.optionalString stdenv.isLinux "-lgcc_s";
 
-  postPatch = optionalString (x11Support && (tix != null)) ''
+  # Determinism: The interpreter is patched to write null timestamps when compiling python files.
+  # This way python doesn't try to update them when we freeze timestamps in nix store.
+  DETERMINISTIC_BUILD=1;
+  # Determinism: We fix the hashes of str, bytes and datetime objects.
+  PYTHONHASHSEED=0;
+
+  postPatch = ''
+    # Determinism
+    substituteInPlace "Lib/py_compile.py" --replace "source_stats['mtime']" "(1 if 'DETERMINISTIC_BUILD' in os.environ else source_stats['mtime'])"
+#     # We do not patch `Lib/importlib/_bootstrap_external.py` because it does not exist.
+  '' + optionalString (x11Support && (tix != null)) ''
     substituteInPlace "Lib/tkinter/tix.py" --replace "os.environ.get('TIX_LIBRARY')" "os.environ.get('TIX_LIBRARY') or '${tix}/lib'"
   '';
 
@@ -80,12 +90,17 @@ in stdenv.mkDerivation {
       fi
     done
     touch $out/lib/python${majorVersion}/test/__init__.py
+
     ln -s "$out/include/python${majorVersion}m" "$out/include/python${majorVersion}"
     paxmark E $out/bin/python${majorVersion}
 
     # Python on Nix is not manylinux1 compatible. https://github.com/NixOS/nixpkgs/issues/18484
     echo "manylinux1_compatible=False" >> $out/lib/${libPrefix}/_manylinux.py
 
+    # Determinism: Windows installers were not deterministic.
+    # We're also not interested in building Windows installers.
+    find "$out" -name 'wininst*.exe' | xargs -r rm -f
+
     # Use Python3 as default python
     ln -s "$out/bin/idle3" "$out/bin/idle"
     ln -s "$out/bin/pip3" "$out/bin/pip"
@@ -93,18 +108,20 @@ in stdenv.mkDerivation {
     ln -s "$out/bin/python3" "$out/bin/python"
     ln -s "$out/bin/python3-config" "$out/bin/python-config"
     ln -s "$out/lib/pkgconfig/python3.pc" "$out/lib/pkgconfig/python.pc"
-  '';
 
-  postFixup = ''
     # Get rid of retained dependencies on -dev packages, and remove
     # some $TMPDIR references to improve binary reproducibility.
+    # Note that the .pyc file of _sysconfigdata.py should be regenerated!
     for i in $out/lib/python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
       sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
     done
 
-    # FIXME: should regenerate this.
-    rm $out/lib/python${majorVersion}/__pycache__/_sysconfigdata.cpython*
-
+    # Determinism: rebuild all bytecode
+    # We exclude lib2to3 because that's Python 2 code which fails
+    # We rebuild three times, once for each optimization level
+    find $out -name "*.py" | $out/bin/python -m compileall -q -f -x "lib2to3" -i -
+    find $out -name "*.py" | $out/bin/python -O -m compileall -q -f -x "lib2to3" -i -
+    find $out -name "*.py" | $out/bin/python -OO -m compileall -q -f -x "lib2to3" -i -
   '';
 
   passthru = let
diff --git a/pkgs/development/interpreters/python/cpython/3.4/default.nix b/pkgs/development/interpreters/python/cpython/3.4/default.nix
index 58e4f21bb4a..b2a4d849c94 100644
--- a/pkgs/development/interpreters/python/cpython/3.4/default.nix
+++ b/pkgs/development/interpreters/python/cpython/3.4/default.nix
@@ -132,6 +132,13 @@ in stdenv.mkDerivation {
     ln -s "$out/bin/python3-config" "$out/bin/python-config"
     ln -s "$out/lib/pkgconfig/python3.pc" "$out/lib/pkgconfig/python.pc"
 
+    # Get rid of retained dependencies on -dev packages, and remove
+    # some $TMPDIR references to improve binary reproducibility.
+    # Note that the .pyc file of _sysconfigdata.py should be regenerated!
+    for i in $out/lib/python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
+      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
+    done
+
     # Determinism: rebuild all bytecode
     # We exclude lib2to3 because that's Python 2 code which fails
     # We rebuild three times, once for each optimization level
@@ -140,18 +147,6 @@ in stdenv.mkDerivation {
     find $out -name "*.py" | $out/bin/python -OO -m compileall -q -f -x "lib2to3" -i -
   '';
 
-  postFixup = ''
-    # Get rid of retained dependencies on -dev packages, and remove
-    # some $TMPDIR references to improve binary reproducibility.
-    for i in $out/lib/python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
-      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
-    done
-
-    # FIXME: should regenerate this.
-    rm $out/lib/python${majorVersion}/__pycache__/_sysconfigdata.cpython*
-
-  '';
-
   passthru = let
     pythonPackages = callPackage ../../../../../top-level/python-packages.nix {python=self; overrides=packageOverrides;};
   in rec {
diff --git a/pkgs/development/interpreters/python/cpython/3.5/default.nix b/pkgs/development/interpreters/python/cpython/3.5/default.nix
index 082f6ff6789..76f445f7a50 100644
--- a/pkgs/development/interpreters/python/cpython/3.5/default.nix
+++ b/pkgs/development/interpreters/python/cpython/3.5/default.nix
@@ -134,6 +134,13 @@ in stdenv.mkDerivation {
     ln -s "$out/bin/python3-config" "$out/bin/python-config"
     ln -s "$out/lib/pkgconfig/python3.pc" "$out/lib/pkgconfig/python.pc"
 
+    # Get rid of retained dependencies on -dev packages, and remove
+    # some $TMPDIR references to improve binary reproducibility.
+    # Note that the .pyc file of _sysconfigdata.py should be regenerated!
+    for i in $out/lib/python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
+      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
+    done
+
     # Determinism: rebuild all bytecode
     # We exclude lib2to3 because that's Python 2 code which fails
     # We rebuild three times, once for each optimization level
@@ -142,17 +149,6 @@ in stdenv.mkDerivation {
     find $out -name "*.py" | $out/bin/python -OO -m compileall -q -f -x "lib2to3" -i -
   '';
 
-  postFixup = ''
-    # Get rid of retained dependencies on -dev packages, and remove
-    # some $TMPDIR references to improve binary reproducibility.
-    for i in $out/lib/python${majorVersion}/_sysconfigdata.py $out/lib/python${majorVersion}/config-${majorVersion}m/Makefile; do
-      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
-    done
-
-    # FIXME: should regenerate this.
-    rm $out/lib/python${majorVersion}/__pycache__/_sysconfigdata.cpython*
-  '';
-
   passthru = let
     pythonPackages = callPackage ../../../../../top-level/python-packages.nix {python=self; overrides=packageOverrides;};
   in rec {
diff --git a/pkgs/development/interpreters/python/cpython/3.6/default.nix b/pkgs/development/interpreters/python/cpython/3.6/default.nix
index 2acca2b8a3c..3c96bf38b6a 100644
--- a/pkgs/development/interpreters/python/cpython/3.6/default.nix
+++ b/pkgs/development/interpreters/python/cpython/3.6/default.nix
@@ -134,6 +134,13 @@ in stdenv.mkDerivation {
     ln -s "$out/bin/python3-config" "$out/bin/python-config"
     ln -s "$out/lib/pkgconfig/python3.pc" "$out/lib/pkgconfig/python.pc"
 
+    # Get rid of retained dependencies on -dev packages, and remove
+    # some $TMPDIR references to improve binary reproducibility.
+    # Note that the .pyc file of _sysconfigdata.py should be regenerated!
+    for i in $out/lib/python${majorVersion}/_sysconfigdata*.py $out/lib/python${majorVersion}/config-${majorVersion}m*/Makefile; do
+      sed -i $i -e "s|-I/nix/store/[^ ']*||g" -e "s|-L/nix/store/[^ ']*||g" -e "s|$TMPDIR|/no-such-path|g"
+    done
+
     # Determinism: rebuild all bytecode
     # We exclude lib2to3 because that's Python 2 code which fails
     # We rebuild three times, once for each optimization level