Immutable dictionaries
This is my first post here. I have strong experience with JavaScript and I'm lucky that I could move forward to Python. What I miss in Python are immutable dictionaries. They are especially useful for configurations and call functions which expect dictionary as argument. In my opinion they would let a place for underlying optimizations. I'd like to propose also literaling syntax for immutable dictionaries. immutable_dict = ( 'key1' : 'value1', 'key2' : 'value2' ) This syntax is not ambiguous with expression statements and tuple literals, but it requires a bit lookahed during the parsing. I would appreciate your opinions on the topic. Most interesting for me is why they are not already part of the language? Kind regards, Asen Bozhilov
https://www.python.org/dev/peps/pep-0416/
Also: https://pypi.python.org/pypi/frozendict
On Wed, Nov 29, 2017 at 9:30 AM, Asen Bozhilov
This is my first post here. I have strong experience with JavaScript and I'm lucky that I could move forward to Python. What I miss in Python are immutable dictionaries. They are especially useful for configurations and call functions which expect dictionary as argument. In my opinion they would let a place for underlying optimizations.
I'd like to propose also literaling syntax for immutable dictionaries.
immutable_dict = ( 'key1' : 'value1', 'key2' : 'value2' )
This syntax is not ambiguous with expression statements and tuple literals, but it requires a bit lookahed during the parsing.
I would appreciate your opinions on the topic. Most interesting for me is why they are not already part of the language?
Kind regards, Asen Bozhilov
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David Mertz wrote:
PEP 351 (also rejected) is related to this. -Barry
On Wed, Nov 29, 2017, at 12:30, Asen Bozhilov wrote:
I would appreciate your opinions on the topic. Most interesting for me is why they are not already part of the language?
See the rejection notes at https://www.python.org/dev/peps/pep-0416/
2017-11-29 18:30 GMT+01:00 Asen Bozhilov
I'd like to propose also literaling syntax for immutable dictionaries.
immutable_dict = ( 'key1' : 'value1', 'key2' : 'value2' )
Since Python 3.3, you can write: vstinner@apu$ python3 Python 3.6.3 (default, Oct 9 2017, 12:07:10)
import types immutable_dict = types.MappingProxyType({"key": "value"})
immutable_dict.pop('key') AttributeError: 'mappingproxy' object has no attribute 'pop'
immutable_dict['key'] = 'value2' TypeError: 'mappingproxy' object does not support item assignment
immutable_dict['key2'] = 'value3' TypeError: 'mappingproxy' object does not support item assignment
Maybe not the ideal syntax, but it already works without having to modify the Python syntax, and it works on Python 3.3 and newer ;-) Victor
On 29/11/2017 17:30, Asen Bozhilov wrote:
This is my first post here. I have strong experience with JavaScript and I'm lucky that I could move forward to Python. What I miss in Python are immutable dictionaries. They are especially useful for configurations and call functions which expect dictionary as argument. In my opinion they would let a place for underlying optimizations.
I'd like to propose also literaling syntax for immutable dictionaries.
immutable_dict = ( 'key1' : 'value1', 'key2' : 'value2' )
This syntax is not ambiguous with expression statements and tuple literals, but it requires a bit lookahed during the parsing.
This is sort of a subset of an idea I once posted on Python-Ideas: Dictionaries, sets and lists (etc. ?) could have a mutable flag, and once it was set to False you could neither change it back nor change the object. (OK there might be some backdoor hacks, this is Python.) This would avoid having to explain to beginners "Why does Python have lists and tuples?" because instead of a tuple, all you need is an immutable list. (Or if you prefer, instead of a list, all you need is a mutable tuple.) Rob Cliffe
2017-11-30 2:16 GMT+01:00 Rob Cliffe
This is sort of a subset of an idea I once posted on Python-Ideas: Dictionaries, sets and lists (etc. ?) could have a mutable flag, and once it was set to False you could neither change it back nor change the object. (OK there might be some backdoor hacks, this is Python.) This would avoid having to explain to beginners "Why does Python have lists and tuples?" because instead of a tuple, all you need is an immutable list. (Or if you prefer, instead of a list, all you need is a mutable tuple.)
Here is a concept implementation of a freeze() function which does something similar. Rather than mutating the mutable object to become immutable, it makes an immutable copy.
freeze({"x": [1,2,{3,4}]}) mappingproxy({'x': (1, 2, frozenset({3, 4}))})
https://gist.github.com/stephanh42/d277170dd8a3a2f026c272a4fda15396 Stephan
Rob Cliffe
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participants (7)
-
Asen Bozhilov -
Barry Warsaw -
David Mertz -
Random832 -
Rob Cliffe -
Stephan Houben -
Victor Stinner