bpo-37892: Use space indents in IDLE Shell (GH-25678)

Adding a newline to the prompt moves it out of the way of
user code input, which now starts at the left margin,
along with continuation lines.

Lib/idlelib/NEWS.txt

@@ -4,6 +4,13 @@ Released on 2021-10-04?
 =========================
 
 
+bpo-37892: Change Shell input indents from tabs to spaces.
+
+bpo-37903: Move the Shell input prompt to a side bar.
+
+bpo-43655: Make window managers on macOS and X Window recognize
+IDLE dialog windows as dialogs.
+
 bpo-43283: Document why printing to IDLE's Shell is often slower than
 printing to a system terminal and that it can be made faster by
 pre-formatting a single string before printing.

Lib/idlelib/pyshell.py

@@ -889,11 +889,11 @@ class PyShell(OutputWindow):
 
         OutputWindow.__init__(self, flist, None, None)
 
-        self.usetabs = True
+        self.usetabs = False
         # indentwidth must be 8 when using tabs.  See note in EditorWindow:
-        self.indentwidth = 8
+        self.indentwidth = 4
 
-        self.sys_ps1 = sys.ps1 if hasattr(sys, 'ps1') else '>>> '
+        self.sys_ps1 = sys.ps1 if hasattr(sys, 'ps1') else '>>>\n'
         self.prompt_last_line = self.sys_ps1.split('\n')[-1]
         self.prompt = self.sys_ps1  # Changes when debug active
 

Misc/NEWS.d/next/IDLE/2021-04-29-02-40-41.bpo-37892.bgW2fk.rst

@@ -0,0 +1 @@
+Indent IDLE Shell input with spaces instead of tabs