with ... : for ... : in a single line

Question

As a beginner python programmer, I am hoping this is some stupid error (or lack of understanding) that has an simple solution:

/tmp> python3 -c 'with open("t","r") as f: for l in f: print(l)'
  File "<string>", line 1
    with open("t","r") as f: for l in f: print(l)
                               ^
SyntaxError: invalid syntax

I can embed a newline in the oneline, but trying to understand why the above does not work

/tmp> python3 -c $'with open("t","r") as f:\n for l in f: print(l)'
Hi there

Or http://stackoverflow.com/questions/2043453/executing-python-multi-line-statements-in-the-one-line-command-line — Thierry Lathuille, Apr 10 '17 at 17:33
@juanpa.arrivillaga, sure you can. For example, `if True: import math; pass; assert 2+2==4` has four statements on the same line. — Kevin, Apr 10 '17 at 17:38
@Kevin Yes, you are correct, the term I needed to use was *simple statement*. Er, rather, you can't have two non-simple statements or non-small statements. — juanpa.arrivillaga, Apr 10 '17 at 17:44

score 1 · Accepted Answer · answered Apr 10 '17 at 17:34

Looking at the Full grammar specification, the only statements you're allowed to put immediately after a with statement on the same line, are statements in the simple_stmt class.

Relevant parts of the grammar:

with_stmt: 'with' with_item (',' with_item)*  ':' suite
suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE
small_stmt: (expr_stmt | del_stmt | pass_stmt | flow_stmt |
             import_stmt | global_stmt | nonlocal_stmt | assert_stmt)
flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt

In plainer language, these statements appear to be:

Expression statements
del
pass
break
continue
return
raise
yield
import
global
nonlocal
assert

for is not part of this list, so it is not allowed to come immediately after a with with no intervening newline.

with ... : for ... : in a single line

1 Answers1