Whitespace-only lines in PDB cause a line continuation when taken from history

[treyhunner]

Bug report

Bug description:

The issue happens only when pulling a line from history.

Typing 4 spaces or a Tab and hitting Enter when at the PDB prompt is interpreted the same as hitting Enter without entering whitespace.
However, grabbing a whitespace-only line from history causes a prompt/line continuatin.

To reproduce:

1. Type if True: and hit Enter
2. Type 4 spaces and hit Enter
3. Type 4 spaces, print("True") and hit Enter twice
4. Hit the up arrow 2 times
5. Hit Enter again

After those 5 steps you will see:

Repeatedly hitting Enter at that point shows the same continuation prompt:

The new REPL had a somewhat similar issue (#118911 was part of it).

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-125378: Trigger a repeat for the full multi-line statement for empty line command #125717
• [3.13] gh-125378: Trigger a repeat for the full multi-line statement for empty line command (GH-125717) #125736

[savannahostrowski]

cc: @gaogaotiantian

[gaogaotiantian]

It doesn't need a repro this complicated :) The repro could be:

1. type any multi-line statement and finish it
2. hit <enter>

Basically the issue is, an empty line means "repeat" in pdb (inherited from cmd.Cmd), but pdb did not remember the full multi-line statement, it only remembers the first line. So equivalently, when you read the empty line from the history, you just sent a "repeat" command, and it repeated the line of the if statement - that line did not end, so pdb is expecting more code, hence the ....

Fix was straightforward - just let pdb remember the full multi-line command as the last command.