Add Access Most Recent Return Value In REPL as a Python TIL

python/access-most-recent-return-value-in-repl.md

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+# Access Most Recent Return Value In REPL
+
+One of my favorite features of Ruby's `irb` and `pry` are that you can use `_`
+to reference the most recent return value. Often as we use an interpreter or
+REPL, we end up with _intermediate_ values. That is, we've execute some kind of
+statement which returned a value and we now want to use that resulting value in
+our next statement. Python also supports `_`.
+
+Let's say I've run a statement that took a while to process, but I forgot to
+assign it to a variable. Instead of re-running the whole thing, I can create a
+variable that references the previous return value using `_`.
+
+```python
+>>> BytePairEncoding.train_bpe(long_text)
+{'merge_rules': [...], 'vocab': {...}}
+>>> result = _
+>>> list(result.keys())
+['merge_rules', 'vocab']
+```
+
+Even if I don't necessarily want to assign it a variable, it can be nice to
+reference the previous value as I continue with what I'm doing:
+
+```python
+>>> result['merge_rules'][0][1]
+256
+>>> result['vocab'][_]
+b'e '
+```
+
+Notice how the value from the first statement gets used as part of a `dict`
+access.
+
+[source](https://docs.python.org/3/tutorial/introduction.html#numbers)