Mailing List Archive: Match statement with literal strings

Match statement with literal strings

Jun 7, 2023, 3:18 PM

Post #1 of 4 (150 views)

This gives the expected results:

with open(data_file, newline="") as reader:
csvreader = csv.DictReader(reader)
for row in csvreader:
#print(row)
match row[RULE_TYPE]:
case "RANGE":
print("range")
case "MANDATORY":
print("mandatory")
case _:
print("nothing to do")

This:

RANGE = "RANGE"
MANDATORY = "MANDATORY"
with open(data_file, newline="") as reader:
csvreader = csv.DictReader(reader)
for row in csvreader:
#print(row)
match row[RULE_TYPE]:
case RANGE:
print("range")
case MANDATORY:
print("mandatory")
case _:
print("nothing to do")

Gives (and I don't understand why):

SyntaxError: name capture 'RANGE' makes remaining patterns unreachable
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Re: Match statement with literal strings [ In reply to ]

python-list at python

Jun 7, 2023, 4:58 PM

Post #2 of 4 (150 views)

Permalink

On 8/06/23 10:18 am, Jason Friedman wrote:
> SyntaxError: name capture 'RANGE' makes remaining patterns unreachable

The bytecode compiler doesn't know that you intend RANGE
to be a constant -- it thinks it's a variable to bind a
value to.

To make this work you need to find a way to refer to the
value that isn't just a bare name. One way would be to
define your constants using an enum:

class Options(Enum):
RANGE = "RANGE"
MANDATORY = "MANDATORY"

match stuff:
case Options.RANGE:
...
case Options.MANDATORY:
...

--
Greg

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Re: Match statement with literal strings [ In reply to ]

python-list at python

Jun 7, 2023, 5:01 PM

Post #3 of 4 (150 views)

Permalink

On Thu, 8 Jun 2023 at 08:19, Jason Friedman via Python-list
<python-list@python.org> wrote:
>
> This gives the expected results:
>
> with open(data_file, newline="") as reader:
> csvreader = csv.DictReader(reader)
> for row in csvreader:
> #print(row)
> match row[RULE_TYPE]:
> case "RANGE":
> print("range")
> case "MANDATORY":
> print("mandatory")
> case _:
> print("nothing to do")
>
> This:
>
> RANGE = "RANGE"
> MANDATORY = "MANDATORY"
> with open(data_file, newline="") as reader:
> csvreader = csv.DictReader(reader)
> for row in csvreader:
> #print(row)
> match row[RULE_TYPE]:
> case RANGE:
> print("range")
> case MANDATORY:
> print("mandatory")
> case _:
> print("nothing to do")
>
> Gives (and I don't understand why):
>
> SyntaxError: name capture 'RANGE' makes remaining patterns unreachable

It's being as clear as it can. When you say "case RANGE:", that is not
a literal, that is a name capture. Check the docs and examples for
case statements for more details.

ChrisA
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Re: Match statement with literal strings [ In reply to ]

python-list at python

Jun 7, 2023, 5:44 PM

Post #4 of 4 (150 views)

Permalink

>
> The bytecode compiler doesn't know that you intend RANGE
> to be a constant -- it thinks it's a variable to bind a
> value to.
>
> To make this work you need to find a way to refer to the
> value that isn't just a bare name. One way would be to
> define your constants using an enum:
>
> class Options(Enum):
> RANGE = "RANGE"
> MANDATORY = "MANDATORY"
>
> match stuff:
> case Options.RANGE:
> ...
> case Options.MANDATORY:
> ...
>

Got it, thank you.

On Wed, Jun 7, 2023 at 6:01?PM Greg Ewing via Python-list <
python-list@python.org> wrote:

> On 8/06/23 10:18 am, Jason Friedman wrote:
> > SyntaxError: name capture 'RANGE' makes remaining patterns unreachable
>
> The bytecode compiler doesn't know that you intend RANGE
> to be a constant -- it thinks it's a variable to bind a
> value to.
>
> To make this work you need to find a way to refer to the
> value that isn't just a bare name. One way would be to
> define your constants using an enum:
>
> class Options(Enum):
> RANGE = "RANGE"
> MANDATORY = "MANDATORY"
>
> match stuff:
> case Options.RANGE:
> ...
> case Options.MANDATORY:
> ...
>
> --
> Greg
>
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>
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