The '<' operator is reserved for future use

The error

PS> python - <<'EOF'
At line:1 char:11
+ python - <<'EOF'
+           ~
Missing file specification after redirection operator.
At line:1 char:10
+ python - <<'EOF'
+          ~
The '<' operator is reserved for future use.

Windows PowerShell 5.1 prints both messages. PowerShell 7 finds the same two, but its default error view shows only the first: ParserError: Missing file specification after redirection operator.

Why it happens

<<'EOF' is bash syntax for "feed the following lines to the command". PowerShell has no heredoc, and it doesn't use < for input at all. It reads the first < as an operator it hasn't implemented, and the second as a redirection with no file after it. Coding agents trained mostly on bash reach for a heredoc whenever they want to run a few lines of Python.

The fix

PowerShell's equivalent is a here-string, piped to python -:

@'
name = "world"
print(f"hello, {name}")
'@ | python -

• @' and '@ must each sit on a line of their own, with '@ at the start of its line.
• The single-quoted form keeps $ and backticks as they are, as <<'EOF' does in bash.
• Avoid python -c @'...'@: PowerShell 7 passes it through, but Windows PowerShell 5.1 strips the double quotes inside, and Python stops with SyntaxError: '(' was never closed.
• Windows PowerShell 5.1 also pipes text to programs as ASCII by default, so é or → arrives as ?.

For anything longer, or with non-ASCII text, write the code to a .py file and run the file. Nothing on the way rewrites a file.