Import large package lazily to speed up startup (#5636)

* Import large package lazily to speed up startup

* Make all jsonschema imports lazy

src/pretix/base/models/auth.py

@@ -53,7 +53,6 @@ from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _
 from django_otp.models import Device
 from django_scopes import scopes_disabled
-from webauthn.helpers.structs import PublicKeyCredentialDescriptor
 
 from pretix.base.i18n import language
 from pretix.helpers.urls import build_absolute_uri
@@ -708,6 +707,8 @@ class U2FDevice(Device):
 
     @property
     def webauthndevice(self):
+        from webauthn.helpers.structs import PublicKeyCredentialDescriptor
+
         d = json.loads(self.json_data)
         return PublicKeyCredentialDescriptor(websafe_decode(d['keyHandle']))
 
@@ -737,6 +738,8 @@ class WebAuthnDevice(Device):
 
     @property
     def webauthndevice(self):
+        from webauthn.helpers.structs import PublicKeyCredentialDescriptor
+
         return PublicKeyCredentialDescriptor(websafe_decode(self.credential_id))
 
     @property

src/pretix/base/models/seating.py

@@ -22,7 +22,6 @@
 import json
 from collections import namedtuple
 
-import jsonschema
 from django.contrib.staticfiles import finders
 from django.core.exceptions import ValidationError
 from django.db import models
@@ -38,6 +37,8 @@ from pretix.base.models import Event, Item, LoggedModel, Organizer, SubEvent
 @deconstructible
 class SeatingPlanLayoutValidator:
     def __call__(self, value):
+        import jsonschema
+
         if not isinstance(value, dict):
             try:
                 val = json.loads(value)

src/pretix/base/models/tax.py

@@ -23,7 +23,6 @@ import json
 from decimal import Decimal
 from typing import Optional
 
-import jsonschema
 from django.contrib.staticfiles import finders
 from django.core.exceptions import ValidationError
 from django.core.validators import MaxValueValidator, MinValueValidator
@@ -298,6 +297,8 @@ def cc_to_vat_prefix(country_code):
 @deconstructible
 class CustomRulesValidator:
     def __call__(self, value):
+        import jsonschema
+
         if not isinstance(value, dict):
             try:
                 val = json.loads(value)