On 21/07/2020 21:00, Eric V. Smith wrote:
On 7/21/2020 2:54 PM, Alex Hall wrote:
It should do the import for you. As was proposed:
```
print(f"My dict: {d!p}")
```
should be equivalent to
```
import pprint
print(f"My dict: {pprint.pformat(d)}")
```
The import should happen in the same scope. Modifying the global
namespace could be confusing.
A quick test shows that adding `import pprint` to
`pprint.pformat({1:2})` slows things down by about 4% on my machine,
which I don't think is worth being concerned about. If the dict has
100 elements, the difference becomes too small to measure.
My first instinct is that monkeypatching the pprint module should
affect !p, but I see that monkeypatching builtins.repr doesn't affect
!r, so I'm not sure.
f-strings call PyObject_Repr directly, without going through builtins.
If we added !p as described here, we'd need to call import every time
we execute !p, because we don't know if it's been imported yet. At
runtime, we'd call "pformat()" via sys.modules['pprint'] after the
import. That could of course be monkey patched.
But I'm still not sure this is a good idea. I can't find the issue on
bpo where this was mentioned, but some of the issues that spring to
mind are:
- Most pprint output is multi-line. Is that a good thing with f-strings?
Why not? f-strings (as of course you know) can already contain multiple
lines, even if the usage is not frequent. ISTM this objection has no
substance.
- How to handle parameters to pprint.pformat()?
This doesn't seem insurmountable. IIUC the relevant parameters are
indent, width, depth, compact, sort_dicts. They could be added after
`!p` separated by some separator - let's say comma for the sake of
argument - with absent parameters taking the default values. So e.g.
!p2 # means indent=2
!p,60 # means width=60. Etc.
If the pformat API were ever changed, adding extra parameters would not
cause backward incompatibility. Removing parameters or changing their
order would, but both seem extremely unlikely to me (YMMV) and I expect
users of !p could live with that.
- Is pprint.pformat() extensible enough? Can an object control how it
is pretty printed?
I'm not sure if I fully understand this objection. It seems to be
suggesting a deficiency in the current pprint.pformat. The proposal
would not change anything here.
I'm sure there are others.
Could you specify.?
I'm not saying I'm +1 on the proposal. Just that there don't seem to be
any insurmountable obstacles to it. My greatest unease is an implicit
import. Are there other areas of Python where this happens?
As I've said before, I'd prefer a revamped "pretty formatting"
library, probably using singledispatch for extensibility. But even
with that, issues like parameterizing the output remain.
Eric
On Tue, Jul 21, 2020 at 8:04 PM Rob Cliffe via Python-ideas
<python-ideas@python.org <mailto:python-ideas@python.org>> wrote:
That seems like a nice idea, but what would happen if pprint had not
been imported? NameError?
Rob Cliffe
On 16/07/2020 05:34, Charles Machalow wrote:
> Right now in str.format(), we have !s, !r, and !a to allow us
to call str(), repr(), and ascii() respectively on the given
expression.
>
> I'm proposing that we add a !p conversion to have
pprint.pformat() be called to convert the given expression to a
'pretty' string.
>
> Calling
> ```
> print(f"My dict: {d!p}")
> ```
>
> is a lot more concise than:
>
> ```
> import pprint
> print(f"My dict: {pprint.pformat(d)}")
> ```
>
> We may even be able to have a static attribute stored to change
the various default kwargs of pprint.pformat().
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