Unable to get the else while parsing through AST module

[bikrammehra97]

BPO	44177
Nosy	@ericvsmith, @lysnikolaou

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-05-20.12:08:24.679>
created_at = <Date 2021-05-19.09:49:02.635>
labels = ['interpreter-core', 'invalid', 'type-feature', '3.7']
title = 'Unable to get the else while parsing through AST module'
updated_at = <Date 2021-05-20.12:08:24.678>
user = 'https://bugs.python.org/bikrammehra97'

bugs.python.org fields:

activity = <Date 2021-05-20.12:08:24.678>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2021-05-20.12:08:24.679>
closer = 'eric.smith'
components = ['Parser']
creation = <Date 2021-05-19.09:49:02.635>
creator = 'bikrammehra97'
dependencies = []
files = []
hgrepos = []
issue_num = 44177
keywords = []
message_count = 6.0
messages = ['393941', '393947', '393949', '393950', '394016', '394018']
nosy_count = 3.0
nosy_names = ['eric.smith', 'lys.nikolaou', 'bikrammehra97']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue44177'
versions = ['Python 3.7']

[bikrammehra97]

Hi Team,

I was parsing python file using AST module but ran into a situation where the else statement is not found in the parsed data.

---------------------
Module used is: ast
---------------------

In the parsed data I can see "if" followed by "elif" but the "else" part I am not able to see.

Sample code used:
---------------------

sample_data = """
if num > 0:
    print("Positive number")
elif num == 0:
    print("Zero")
else:
    print("Negative number")
"""
---------------------

tree = ast.parse(sample_data )

The above code provide me below data in ast.dump(tree)

Module(body=[If(test=Compare(left=Name(id='num', ctx=Load()), ops=[Gt()], comparators=[Constant(value=0, kind=None)]), body=[Expr(value=Call(func=Name(id='print', ctx=Load()), args=[Constant(value='Positive number', kind=None)], keywords=[]))], orelse=[If(test=Compare(left=Name(id='num', ctx=Load()), ops=[Eq()], comparators=[Constant(value=0, kind=None)]), body=[Expr(value=Call(func=Name(id='print', ctx=Load()), args=[Constant(value='Zero', kind=None)], keywords=[]))], orelse=[Expr(value=Call(func=Name(id='print', ctx=Load()), args=[Constant(value='Negative number', kind=None)], keywords=[]))])])], type_ignores=[])

While I was traversing through this tree I can't see else in the structure because it is subpart of orelse i.e. inside elif part.

Doc referred is : https://docs.python.org/3/library/ast.html

Thanks and Best Regards,
Bikram

[ericvsmith]

Formatting the result, I get:
Module(body=[If(test=Compare(left=Name(id='num', ctx=Load()),
ops=[Gt()],
comparators=[Constant(value=0, kind=None)]),
body=[Expr(value=Call(func=Name(id='print', ctx=Load()),
args=[Constant(value='Positive number',
kind=None)],
keywords=[]))],
orelse=[If(test=Compare(left=Name(id='num', ctx=Load()),
ops=[Eq()],
comparators=[Constant(value=0, kind=None)]),
body=[Expr(value=Call(func=Name(id='print', ctx=Load()),
args=[Constant(value='Zero', kind=None)],
keywords=[]))],
orelse=[Expr(value=Call(func=Name(id='print', ctx=Load()),
args=[Constant(value='Negative number', kind=None)],
keywords=[]))])])],
type_ignores=[])

You'll have to extract the "else" part by walking the tree yourself.

I was parsing python file using AST module but ran into a situation where the else statement is not found in the parsed data.

It is in the parsed data, though. Just not directly in the "If" node.

[bikrammehra97]

Hi Eric,

Thanks for the quick response here,

I have gone through your suggestion but following that I am able to print the else node data i.e. "print("Negative number")" but unable to get the lineno of that else child node.

Could you please confirm if there is a way in AST where I can get the lineno of the else child node.

Thanks and Best Regards,
Bikram

[ericvsmith]

It's in the AST.

>>> tree.body[0].orelse[0].orelse[0].lineno
7

To see it with dump, use: ast.dump(tree, include_attributes=True)

Which, after some reformatting, gives:

Module(body=[If(test=Compare(left=Name(id='num', ctx=Load(), lineno=2, col_offset=3, end_lineno=2, end_col_offset=6),
ops=[Gt()], comparators=[Constant(value=0, kind=None, lineno=2, col_offset=9, end_lineno=2, end_col_offset=10)],
lineno=2, col_offset=3, end_lineno=2, end_col_offset=10),
body=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=3, col_offset=4, end_lineno=3, end_col_offset=9),
args=[Constant(value='Positive number', kind=None, lineno=3, col_offset=10, end_lineno=3, end_col_offset=27)],
keywords=[], lineno=3, col_offset=4, end_lineno=3, end_col_offset=28),
lineno=3, col_offset=4, end_lineno=3, end_col_offset=28)],
orelse=[If(test=Compare(left=Name(id='num', ctx=Load(), lineno=4, col_offset=5, end_lineno=4, end_col_offset=8),
ops=[Eq()],
comparators=[Constant(value=0, kind=None, lineno=4, col_offset=12, end_lineno=4, end_col_offset=13)], lineno=4, col_offset=5, end_lineno=4, end_col_offset=13),
body=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=5, col_offset=4, end_lineno=5, end_col_offset=9),
args=[Constant(value='Zero', kind=None, lineno=5, col_offset=10, end_lineno=5, end_col_offset=16)],
keywords=[], lineno=5, col_offset=4, end_lineno=5, end_col_offset=17),
lineno=5, col_offset=4, end_lineno=5, end_col_offset=17)],
orelse=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=7, col_offset=4, end_lineno=7, end_col_offset=9),
args=[Constant(value='Negative number', kind=None, lineno=7, col_offset=10, end_lineno=7, end_col_offset=27)],
keywords=[], lineno=7, col_offset=4, end_lineno=7, end_col_offset=28),
lineno=7, col_offset=4, end_lineno=7, end_col_offset=28)], lineno=4, col_offset=0, end_lineno=7, end_col_offset=28)],
lineno=2, col_offset=0, end_lineno=7, end_col_offset=28)], type_ignores=[])"

I don't think there's any enhancement to be made here, so I'm going to close this issue.

[bikrammehra97]

Hi Eric,

I have tried the action plan suggested by you in your last comment, but below are my logs and still I am unable to get lineno for else statement.

----The respective line no for each line are below ----

1
2 if num > 0:
3 print("Positive number")
4 elif num == 0:
5 print("Zero")
6 else:
7 print("Negative number")

The re-formatted dump is as below and doesn't have lineno for else statement

Module(body=[If(test=Compare(left=Name(id='num', ctx=Load(), lineno=2, col_offset=3, end_lineno=2, end_col_offset=6),
ops=[Gt()], comparators=[Constant(value=0, kind=None, lineno=2, col_offset=9, end_lineno=2, end_col_offset=10)], lineno=2, col_offset=3, end_lineno=2, end_col_offset=10),
body=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=3, col_offset=4, end_lineno=3, end_col_offset=9), args=[Constant(value='Positive number', kind=None, lineno=3, col_offset=10, end_lineno=3,
end_col_offset=27)],
keywords=[], lineno=3, col_offset=4, end_lineno=3, end_col_offset=28),
lineno=3, col_offset=4, end_lineno=3, end_col_offset=28)],
orelse=[If(test=Compare(left=Name(id='num', ctx=Load(), lineno=4, col_offset=5, end_lineno=4, end_col_offset=8),
ops=[Eq()],
comparators=[Constant(value=0, kind=None, lineno=4, col_offset=12, end_lineno=4,
end_col_offset=13)], lineno=4, col_offset=5, end_lineno=4, end_col_offset=13),
body=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=5, col_offset=4, end_lineno=5, end_col_offset=9),
args=[Constant(value='Zero', kind=None, lineno=5, col_offset=10, end_lineno=5,
end_col_offset=16)],
keywords=[], lineno=5, col_offset=4, end_lineno=5, end_col_offset=17), lineno=5, col_offset=4, end_lineno=5, end_col_offset=17)],
orelse=[Expr(value=Call(func=Name(id='print', ctx=Load(), lineno=7, col_offset=4, end_lineno=7, end_col_offset=9),
args=[Constant(value='Negative number', kind=None, lineno=7, col_offset=10, end_lineno=7, end_col_offset=27)],
keywords=[], lineno=7, col_offset=4, end_lineno=7, end_col_offset=28),
lineno=7, col_offset=4, end_lineno=7, end_col_offset=28)], lineno=4, col_offset=0, end_lineno=7,
end_col_offset=28)],
lineno=2, col_offset=0, end_lineno=7, end_col_offset=28)], type_ignores=[])

If we use tree to get the lineno then its giving as below
tree.body[0].orelse[0].orelse[0].lineno
7

Here the lineno 7 denotes to the body of else statement not the else lineno.

Could you please help me out where you can show the respective line no of else statement i.e. 6 in above example.

Thanks and Best Regards,
Bikram

[ericvsmith]

There's no actual code associated with the "else" line, so there's no way to get the line number. dis.dis(sample_data) might give you some insight.

Since this all works as designed, I'm going to close this issue. You might get more help on StackOverflow or similar.