Repository: ua-parser/uap-python

Issue:
Default / lazy parser not cached
I'm guessing I'm doing something wrong, because it makes very little sense when reading the doc but in short, on my machine, the slowest parser is `ua-parser-rs`.

That's what I'm doing in ipython (but I have the same results just with the python interpreter, it's just easier to time it):

```python
from ua_parser import parse
ua_string = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36'

%timeit parse(ua_string).with_defaults()
```

* With `ua-parser-rs`:

`734 ms ± 27.7 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)`

* With just `google-re2`

`188 ms ± 10.9 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)`

* After I uninstall `ua-parser-rs` and `google-re2`

`1.07 ms ± 33.3 μs per loop (mean ± std. dev. of 7 runs, 1,000 loops each)`

I'm on ubuntu 24.10 with Python 3.12.7.

Do you have any idea what's going on there? Something related to the cache being reloaded on every call? I couldn't find a way to avoid that.

Discussion:
@masklinn: note: I'm leaving the comment for posterity and the information in it is technically true, but it's a reply to a complete misunderstanding of the report, so you can skip it if you're facing the same issue, the comments afterwards are the investigation "proper", and the fix has been released as part of 1.0.1.

> I'm guessing I'm doing something wrong [...] Something related to the cache being reloaded on every call? I couldn't find a way to avoid that.

For what that's worth[^0] *only the basic python parser is cached by default*[^1]: on my benchmarks while a (sufficiently large) cache does improve the performance of the native parsers I considered the additional memory not really worth it given what little effect it had on what I considered a real-world benchmark.

Since you're looping on a single user agent string, it makes sense that the one cached parser would be faster than the two natives, as it's basically an ideal situation for a cache (once the UA has been parsed once future calls are just a cache hit), however the difference in scale you report is significantly larger than I would have expected, and so is the difference between re2 and regex. I'll have to see how ipython interacts with things when I'm able.

In the meantime, could you provide details for the machine you're running things on? (e.g. CPU model / architecture) I've mostly been benching on my dev machine (might have been smart to have some benches I could run on GHA, I should do that).

And could you try the bench script provided with ua-parser? Most of my benchmarking has been done using https://raw.githubusercontent.com/ua-parser/uap-python/refs/heads/master/samples/useragents.txt so I'd be grateful if you could download that file and run

    python -mua_parser bench useragents.txt

Then maybe try to run a pared down configuration on [id.txt](https://github.com/user-attachments/files/18621898/id.txt) (that's the same user agent repeated 100000 times):

    python -mua_parser bench id.txt --caches none sieve --cachesizes 1

note that it might take a fairly long time (possibly minutes)

[^0]: it's documented but not made super clear in the readme as I assumed it wouldn't generally be visible or relevant
[^1]: you can create a custom parser with caching though, cf [cache and other advanced parser customisations](https://uap-python.readthedocs.io/stable/guides.html#cache-and-other-advanced-parser-customisation) in the documentation@Rafiot: For context, my real-world use-case is here: https://github.com/Lookyloo/lookyloo/blob/main/lookyloo/helpers.py#L389
It is triggered when I submit a URL to capture, don't specify a user agent, fallback to the default one from chromium, which is then parsed.
I noticed the API took ~1s to respond when it should be immediate (and it is with the basic python parser). 

Either way, it's not really relevant in this context, and the amount of UAs I need to parse doesn't require anything highly performant, but I have long running processes so I'm happy to use the rust parser, if I can make sure it is loaded only once.

And I think it is the way to go (?):

```python
import ua_parser

base = ua_parser.regex.Resolver(ua_parser.loaders.load_lazy_builtins())
ua_parser.parser = ua_parser.Parser(base)
ua_string = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36'

%timeit ua_parser.parse(ua_string).with_defaults()

```

=> `24 μs ± 383 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)`


-------------

CPU on my machine: Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz / x86_64
CPU on the server: Intel(R) Xeon(R) CPU E5-2640 v3 @ 2.60GHz / x86_64

-------------

<details>
<summary>Benchmarks (on my machine)</summary>

```
useragents.txt: 75158 lines, 20322 unique (27%)
basic              : 50.65s ( 674us/line)
basic-lru-10       : 52.29s ( 696us/line)
basic-lru-20       : 52.49s ( 698us/line)
basic-lru-50       : 51.95s ( 691us/line)
basic-lru-100      : 50.82s ( 676us/line)
basic-lru-200      : 47.56s ( 633us/line)
basic-lru-500      : 41.02s ( 546us/line)
basic-lru-1000     : 34.04s ( 453us/line)
basic-lru-2000     : 28.64s ( 381us/line)
basic-lru-5000     : 20.56s ( 274us/line)
basic-s3fifo-10    : 53.35s ( 710us/line)
basic-s3fifo-20    : 52.96s ( 705us/line)
basic-s3fifo-50    : 47.29s ( 629us/line)
basic-s3fifo-100   : 44.54s ( 593us/line)
basic-s3fifo-200   : 40.24s ( 535us/line)
basic-s3fifo-500   : 34.81s ( 463us/line)
basic-s3fifo-1000  : 30.15s ( 401us/line)
basic-s3fifo-2000  : 25.08s ( 334us/line)
basic-s3fifo-5000  : 18.84s ( 251us/line)
basic-sieve-10     : 56.27s ( 749us/line)
basic-sieve-20     : 53.51s ( 712us/line)
basic-sieve-50     : 48.31s ( 643us/line)
basic-sieve-100    : 44.51s ( 592us/line)
basic-sieve-200    : 40.12s ( 534us/line)
basic-sieve-500    : 34.16s ( 455us/line)
basic-sieve-1000   : 28.32s ( 377us/line)
basic-sieve-2000   : 23.23s ( 309us/line)
basic-sieve-5000   : 18.25s ( 243us/line)
re2                :  4.58s (  61us/line)
re2-lru-10         :  5.02s (  67us/line)
re2-lru-20         :  4.93s (  66us/line)
re2-lru-50         :  5.02s (  67us/line)
re2-lru-100        :  4.57s (  61us/line)
re2-lru-200        :  4.37s (  58us/line)
re2-lru-500        :  3.72s (  50us/line)
re2-lru-1000       :  3.35s (  45us/line)
re2-lru-2000       :  2.69s (  36us/line)
re2-lru-5000       :  2.01s (  27us/line)
re2-s3fifo-10      :  4.65s (  62us/line)
re2-s3fifo-20      :  4.54s (  60us/line)
re2-s3fifo-50      :  4.38s (  58us/line)
re2-s3fifo-100     :  4.03s (  54us/line)
re2-s3fifo-200     :  3.93s (  52us/line)
re2-s3fifo-500     :  3.16s (  42us/line)
re2-s3fifo-1000    :  2.71s (  36us/line)
re2-s3fifo-2000    :  2.31s (  31us/line)
re2-s3fifo-5000    :  1.95s (  26us/line)
re2-sieve-10       :  4.57s (  61us/line)
re2-sieve-20       :  4.63s (  62us/line)
re2-sieve-50       :  4.33s (  58us/line)
re2-sieve-100      :  4.14s (  55us/line)
re2-sieve-200      :  3.73s (  50us/line)
re2-sieve-500      :  3.08s (  41us/line)
re2-sieve-1000     :  2.65s (  35us/line)
re2-sieve-2000     :  2.31s (  31us/line)
re2-sieve-5000     :  1.84s (  25us/line)
regex              :  2.58s (  34us/line)
regex-lru-10       :  2.75s (  37us/line)
regex-lru-20       :  2.69s (  36us/line)
regex-lru-50       :  2.68s (  36us/line)
regex-lru-100      :  2.62s (  35us/line)
regex-lru-200      :  2.82s (  38us/line)
regex-lru-500      :  2.39s (  32us/line)
regex-lru-1000     :  2.12s (  28us/line)
regex-lru-2000     :  1.74s (  23us/line)
regex-lru-5000     :  1.42s (  19us/line)
regex-s3fifo-10    :  2.94s (  39us/line)
regex-s3fifo-20    :  2.93s (  39us/line)
regex-s3fifo-50    :  2.69s (  36us/line)
regex-s3fifo-100   :  2.54s (  34us/line)
regex-s3fifo-200   :  2.32s (  31us/line)
regex-s3fifo-500   :  1.99s (  27us/line)
regex-s3fifo-1000  :  1.71s (  23us/line)
regex-s3fifo-2000  :  1.46s (  19us/line)
regex-s3fifo-5000  :  1.18s (  16us/line)
regex-sieve-10     :  2.85s (  38us/line)
regex-sieve-20     :  2.88s (  38us/line)
regex-sieve-50     :  2.66s (  35us/line)
regex-sieve-100    :  2.53s (  34us/line)
regex-sieve-200    :  2.27s (  30us/line)
regex-sieve-500    :  1.96s (  26us/line)
regex-sieve-1000   :  1.72s (  23us/line)
regex-sieve-2000   :  1.48s (  20us/line)
regex-sieve-5000   :  1.23s (  16us/line)
legacy             : 45.64s ( 607us/line)
```
</details>@masklinn: > For context, my real-world use-case is here: https://github.com/Lookyloo/lookyloo/blob/main/lookyloo/helpers.py#L389 It is triggered when I submit a URL to capture, don't specify a user agent, fallback to the default one from chromium, which is then parsed. I noticed the API took ~1s to respond when it should be immediate (and it is with the basic python parser).

Oooh I see now, I completely misunderstood your report (probably because mentions of cache kinda prime me with how much time I spent on that), I'm dreadfully sorry, you're talking about caching the parser itself after lazily instantiating it!

At a glance, it looks like I broke the parser memoization in #230: I forgot to keep the assignment of the parser onto the `parser` global: https://github.com/ua-parser/uap-python/commit/6fb7b586479824bc435f2628d568458db1de879d#diff-f71b6cb0226b7966e6f4e7aa9b42e7482dc8eb9410323f3f0536dde7f04130c1L135-R140 That is consistent with what you report:  the regex and re2 parsers have high instantiation overhead because they have to construct the regex filter, whereas the basic / pure python parser pretty much just stores the matchers it's handled.

Thanks for the report! And sorry again for the misunderstanding.

> And I think it is the way to go (?):
> ```python
> import ua_parser
> 
> base = ua_parser.regex.Resolver(ua_parser.loaders.load_lazy_builtins())
> ua_parser.parser = ua_parser.Parser(base)
> ua_string = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.104 Safari/537.36'
> ```

That looks about right, yes. There should actually be a [`from_matchers`](https://uap-python.readthedocs.io/stable/api.html#ua_parser.Parser.from_matchers) method on `ua_parser` which builds the resolver for you using the "best available resolver" heuristics.@Rafiot: Do not worry at all! I should have explained my issue better.

For now, I'll just use the default parser (as it is not blocking), but will go back to the rust one as soon as the bug is fixed: as it's on long running processes, it makes sense to have one long(ish) initialization, and quick parsing.@masklinn: FWIW I just published 1.0.1 which should fix the issue: using your test case (kinda I'm just using timeit at the CLI), on 1.0.0 I get:
- 589 usec per loop on the basic parser
- 85.6 msec per loop on the re2 parser
- 349 msec per loop on the regex parser

Which does track with your observations at least in terms of scaling.

With 1.0.1 off of pypi,
- 1.54 usec per loop on the basic parser
- 24.9 usec per loop on the re2 parser
- 13.6 usec per loop on the regex parser

And thanks yet again for the report, and sorry for the trouble.@Rafiot: Excellent, thank you very much, it works as expected! 

Solution patch:
diff --git a/pyproject.toml b/pyproject.toml
index 161c98b..11425fc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,7 +5,7 @@ build-backend = "setuptools.build_meta"
 [project]
 name = "ua-parser"
 description = "Python port of Browserscope's user agent parser"
-version = "1.0.0"
+version = "1.0.1"
 readme = "README.rst"
 requires-python = ">=3.9"
 dependencies = ["ua-parser-builtins"]
diff --git a/src/ua_parser/__init__.py b/src/ua_parser/__init__.py
index 040dda3..5b5ba71 100644
--- a/src/ua_parser/__init__.py
+++ b/src/ua_parser/__init__.py
@@ -41,7 +41,8 @@
 ]
 
 import importlib.util
-from typing import Callable, Optional
+import threading
+from typing import Callable, Optional, cast
 
 from .basic import Resolver as BasicResolver
 from .caching import CachingResolver, S3Fifo as Cache
@@ -78,7 +79,7 @@
 )
 
 
-VERSION = (1, 0, 0)
+VERSION = (1, 0, 1)
 
 
 class Parser:
@@ -135,15 +136,27 @@ def parse_device(self: Resolver, ua: str) -> Optional[Device]:
 initialisation, rather than pay for it at first call.
 """
 
+_lazy_globals_lock = threading.Lock()
+
 
 def __getattr__(name: str) -> Parser:
     global parser
-    if name == "parser":
-        if RegexResolver or Re2Resolver or IS_GRAAL:
-            matchers = load_lazy_builtins()
-        else:
-            matchers = load_builtins()
-        return Parser.from_matchers(matchers)
+    with _lazy_globals_lock:
+        if name == "parser":
+            # if two threads access `ua_parser.parser` before it's
+            # initialised, the second one will wait until the first
+            # one's finished by which time the parser global should be
+            # set and can be returned with no extra work
+            if p := globals().get("parser"):
+                return cast(Parser, p)
+
+            if RegexResolver or Re2Resolver or IS_GRAAL:
+                matchers = load_lazy_builtins()
+            else:
+                matchers = load_builtins()
+            parser = Parser.from_matchers(matchers)
+            return parser
+
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
 
 


Test patch:
diff --git a/tests/test_convenience_parser.py b/tests/test_convenience_parser.py
index cf1d360..8624061 100644
--- a/tests/test_convenience_parser.py
+++ b/tests/test_convenience_parser.py
@@ -1,6 +1,23 @@
+import ua_parser
 from ua_parser import Domain, Parser, PartialResult, Result
 
 
+def test_parser_memoized() -> None:
+    """The global parser should be lazily instantiated but memoized"""
+    # ensure there is no global parser
+    vars(ua_parser).pop("parser", None)
+
+    p1 = ua_parser.parser
+    p2 = ua_parser.parser
+
+    assert p1 is p2
+
+    # force the creation of a clean parser
+    del ua_parser.parser
+    p3 = ua_parser.parser
+    assert p3 is not p1
+
+
 def resolver(s: str, d: Domain) -> PartialResult:
     return PartialResult(d, None, None, None, s)