Django常见问题集

django2.0发行文档说，django2.0最后一个支持的是python3.4+...

所以，还在用python2.7的同学只能手动指定版本下载了

pip2 install django==1.8.17 或 pip2 install django==1.10

摘自：https://docs.djangoproject.com/en/2.0/releases/2.0/

Python2.7.x 下载django的报错

'''
在新创建的Django项目中执行makemigrations时，遇到：
ValueError: The field admin.LogEntry.user was declared with a lazy reference to 'fault_reporting.userinfo', but app 'fault_reporting' isn't installed.
这类app并没有安装的错误
而仔细观察，这个报错的app名字是我们之前项目中的app名字，但现在却在我们当前的项目中报错了。究其原因，则是因为之前的项目中的app缓存被存在了Django的模块内的"某些地方"
而我们当在新的项目中用到"某些地方"的功能时，执行了之前的缓存内容，从而引发错误
而普通的解决办法，就是删除当前项目中的.idea文件和__pycache__文件，然后就是删除migrations文件下的00开头的py文件都解决不了。甚至是卸载Django重新安装————都没用！
因为我们并没有删除Django模块中"某些地方"的缓存文件(pip uninstall Django都清不了这些缓存文件)。so，我们要手动去删除这这个"某个地方"的缓存文件
打开你的解释器下的Lib\site-packages\django\contrib\admin\migrations
删除除了__init__.py外的其他的文件
然后再次运行makemigrations即可
see also：https://stackoverflow.com/questions/40222268/valueerror-in-django-when-running-the-python-manage-py-migrate-command
'''

makemigrations时遇到ValueError:Related mode 'app01.Userinfo' cannot be resolved

from django.db import models

class UserInfo(models.Model):
    user = models.CharField(max_length=32)
    pwd = models.CharField(max_length=32)

class Token(models.Model):
    user = models.OneToOneField(UserInfo,on_delete=None)
    token = models.CharField(max_length=64)

# 关键字on_delete=None
# 2.0版本在源码中取消了on_delete=None，需要手动传递，

class OneToOneField(ForeignKey):

    def __init__(self, to, on_delete, to_field=None, **kwargs): # 源码中取消默认值
        kwargs['unique'] = True
        super().__init__(to, on_delete, to_field=to_field, **kwargs)


# 而在django1.11.5和1.8.17版本中，都是有默值的
def __init__(self, to, on_delete=None, to_field=None, **kwargs):

django2.x版本关于model在绑定外键的时候，遇到on_delete报错

 1 启动报错：SyntaxError: Generator expression must be parenthesized，有时候，在使用命令python manager.py runserver时，会发先启动失败，报错日志如下：
 2 [root@cs es_demo]# python37 manage.py runserver
 3 Unhandled exception in thread started by .wrapper at 0x7f220f0edae8>
 4 Traceback (most recent call last):
 5   File "/usr/local/python/python37/lib/python3.7/site-packages/django/utils/autoreload.py", line 227, in wrapper
 6     fn(*args, **kwargs)
 7   File "/usr/local/python/python37/lib/python3.7/site-packages/django/core/management/commands/runserver.py", line 117, in inner_run
 8     autoreload.raise_last_exception()
 9   File "/usr/local/python/python37/lib/python3.7/site-packages/django/utils/autoreload.py", line 250, in raise_last_exception
10     six.reraise(*_exception)
11   File "/usr/local/python/python37/lib/python3.7/site-packages/django/utils/six.py", line 685, in reraise
12     raise value.with_traceback(tb)
13   File "/usr/local/python/python37/lib/python3.7/site-packages/django/utils/autoreload.py", line 227, in wrapper
14     fn(*args, **kwargs)
15   File "/usr/local/python/python37/lib/python3.7/site-packages/django/__init__.py", line 27, in setup
16     apps.populate(settings.INSTALLED_APPS)
17   File "/usr/local/python/python37/lib/python3.7/site-packages/django/apps/registry.py", line 85, in populate
18     app_config = AppConfig.create(entry)
19   File "/usr/local/python/python37/lib/python3.7/site-packages/django/apps/config.py", line 94, in create
20     module = import_module(entry)
21   File "/usr/local/python/python37/lib/python3.7/importlib/__init__.py", line 127, in import_module
22     return _bootstrap._gcd_import(name[level:], package, level)
23   File "", line 1006, in _gcd_import
24   File "", line 983, in _find_and_load
25   File "", line 967, in _find_and_load_unlocked
26   File "", line 677, in _load_unlocked
27   File "", line 728, in exec_module
28   File "", line 219, in _call_with_frames_removed
29   File "/usr/local/python/python37/lib/python3.7/site-packages/django/contrib/admin/__init__.py", line 4, in 
30     from django.contrib.admin.filters import (
31   File "/usr/local/python/python37/lib/python3.7/site-packages/django/contrib/admin/filters.py", line 10, in 
32     from django.contrib.admin.options import IncorrectLookupParameters
33   File "/usr/local/python/python37/lib/python3.7/site-packages/django/contrib/admin/options.py", line 12, in 
34     from django.contrib.admin import helpers, widgets
35   File "/usr/local/python/python37/lib/python3.7/site-packages/django/contrib/admin/widgets.py", line 151
36     '%s=%s' % (k, v) for k, v in params.items(),
37     ^
38 SyntaxError: Generator expression must be parenthesized
39 
40 可以发现最后一行提示说是语法错误，说是生成器表达式有问题，那具体的报错行内容是'%s=%s' % (k, v) for k, v in params.items(),，可以看到，最后一个标点符号很有意思，我们找到源码文件对应的行，把这个标点符号去掉即可。
41 ps：如果是pycharm中修改的话，由于这个文件是源码，还要注意提示框中选择I want to edit this file anyway。

Django之启动报错：Generator expression must be parenthesized

 

 

 

 

 

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转载于:https://www.cnblogs.com/Neeo/p/9673000.html