I want to increase the length of the username in django from 30 to around 80, I know it may be duplicate question but the previous answers are not working, for example https://kfalck.net/2010/12/30/longer-usernames-for-django
this is for Django 1.2.
Did anyone try similar hack for Django>1.5
Thanks in advance
In Django 1.5 and above, the recommended approach would be to create a custom user model. Then you can make the username field exactly as you want.
I had the same problem few days ago. Finally, I ended just with cutting off first 30 characters of the (old) username (into the new database table), and adding a custom authentication backend that will check the email instead of user name. Terrible hack I know, and I'm planning to fix it as soon as I have some time. The idea is following:
I already have a model class that has one-to-one relation with djangos auth.User. I will add another field there called full_username.
class MyCustomUserModel(models.Model):
user = models.OneToOneField(
settings.AUTH_USER_MODEL, related_name="custom_user")
full_username = models.CharField(max_length=80, ...)
...
Then, I'll add another custom authentication backend that will check this field as username. It would look something like this:
from django.contrib.auth.backends import ModelBackend
class FullUsernameAuthBackend(ModelBackend):
def authenticate(self, username=None, password=None, **kwargs):
UserModel = get_user_model()
if username is None:
username = kwargs.get(UserModel.USERNAME_FIELD)
try:
user = UserModel._default_manager.filter(custom_user__full_username=username)
# If this doesn't work, will use (the second case):
# user = MyCustomUserModel.objects.filter(full_username=username).user
if user.check_password(password):
return user
except UserModel.DoesNotExist:
# Adding exception MyCustomUserModel.DoesNotExist in "(the second case)"
# Run the default password hasher once to reduce the timing
# difference between an existing and a non-existing user (#20760).
UserModel().set_password(password)
After this, you need to change settings.py:
AUTHENTICATION_BACKENDS = (
"....FullUsernameAuthBackend",
# I will have the email auth backend here also.
)
I hope that it will work.
Custom User Models are a huge change to make and aren't always compatible with apps. I solved it by running this very pragmatic migration. Note this only solves it at the database level.
migrations.RunSQL("alter table auth_user alter column username type varchar(254);")
Related
Is there a simple way to force unique email address's during registration with website built with Django?
I've seen some "addons?" like HMAC, but it seems a bit too complicated for what I am trying to achieve.
Also, would it be possible to accept registration only from a list of domains? (such as only emails from "#google.com")
I had the same problem and solved it by extending the AbstractUser class to my own class MyUser and changing the defaults.
Then by making the this class MyUser as a default model class for all my users I could apply this property(unique E-Mail) to all my users on my web app.
Create an app myuser. There in models.py:
from django.contrib.auth.models import AbstractUser
#create your own user class.
class MyUser(AbstractUser):
def __init__(self, *args, **kwargs):
self._meta.get_field('email').blank = False
self._meta.get_field('email')._unique = True
super(MyUser, self).__init__(*args, **kwargs)
#Changed the defaults above.
#Give any additional field you want to associate your user with.
NOTE: AbstractUser already has all the basic fields you would want a User Model to have. For example: username, password, email etc. Check all of them here.
The last thing you would want to do is add the following in your setting.py
AUTH_USER_MODEL = 'myuser.MyUser'
This will make sure that the default user is associated with your web app is the extended(modified) MyUser class. This will provide you with all the basic functionalities that django provides for a User.
login
logout
in your views: you can get user instance in: request.user
etc.
I would like to suggest that you may need some additional code(in forms.py and views.py) to create a user through this type of class. I hope you will manage that. This should be enough to guide you in the right direction.
Maybe a library would have helped but since you needed an authentication for emails' domains as well, I think this should do the trick. In my humble opinion, you can't always depend on the 3rd party libraries for every other functionality.
Lastly, as you asked to authenticate a user coming only from a domain like #gmail.com or #outlook.com, a simple check in your django forms' clean method would do the trick. I hope you know how to handle django forms. If not, then you can learn about them in the official docs. They are an essential part of Django.
You can check the E-Mail with this logic:
email = self.cleaned_data['email']
email_source = email.split('#')[-1]
#email_source will now have values like: gmail.com, outlook.com etc
#you can now validate email_source now like:
permitted_sources = ['gmail.com' , 'outlook.com' , ]
if email_source in permitted_sources:
return cleaned_data
else:
raise forms.ValidationError('Error Message')
#Note: This logic should be kept in your clean method.
I hope this guides you. Thanks.
I've just integrated Django-Social-Auth (DSA) v0.7.23 using django 1.5 with a custom User model and auth/login is working fine except for the username field which is not being stored in my custom User model.
Stepping through the DSA code it appears to explicitly remove the username which was passed back by facebook. Here is the function in question that pops the username off:
#classmethod
def username_field(cls, values):
user_model = cls.user_model()
if hasattr(user_model, 'USERNAME_FIELD'):
# Django 1.5 custom user model, 'username' is just for internal
# use, doesn't imply that the model should have an username field
values[user_model.USERNAME_FIELD] = values.pop('username') # Username removed
return values
How can I go about getting the username that was passed back from facebook and not having it be explicitly removed by DSA?
I believe a work around would be to create a custom pipeline that generates a username. However I was wondering if anyone else encountered this scenario before and leveraged anything that already exists within DSA (i.e. a particular settings.py configuration)
Thanks.
The original username is available in the details attribute passed to pipeline functions, take this for example:
def generated_username(user, details, *args, **kwargs):
username = details['username']
user.your_field = username
user.save()
It's worth noting that the username is popped from values if you have a USERNAME_FIELD defined in your custom model.
Is there anything wrong with running alter table on auth_user to make username be varchar(75) so it can fit an email? What does that break if anything?
If you were to change auth_user.username to be varchar(75) where would you need to modify django? Is it simply a matter of changing 30 to 75 in the source code?
username = models.CharField(_('username'), max_length=30, unique=True, help_text=_("Required. 30 characters or fewer. Letters, numbers and #/./+/-/_ characters"))
Or is there other validation on this field that would have to be changed or any other repercussions to doing so?
See comment discussion with bartek below regarding the reason for doing it.
Edit: Looking back on this after many months. For anyone who doesn't know the premise: Some apps don't have a requirement or desire to use a username, they use only email for registration & auth. Unfortunately in django auth.contrib, username is required. You could start putting emails in the username field, but the field is only 30 char and emails may be long in the real world. Potentially even longer than the 75 char suggested here, but 75 char accommodates most sane email addresses. The question is aimed at this situation, as encountered by email-auth-based applications.
There's a way to achieve that without touching the core model, and without inheritance, but it's definitely hackish and I would use it with extra care.
If you look at Django's doc on signals, you'll see there's one called class_prepared, which is basically sent once any actual model class has been created by the metaclass. That moment is your last chance of modifying any model before any magic takes place (ie: ModelForm, ModelAdmin, syncdb, etc...).
So the plan is simple, you just register that signal with a handler that will detect when it is called for the User model, and then change the max_length property of the username field.
Now the question is, where should this code lives? It has to be executed before the User model is loaded, so that often means very early. Unfortunately, you can't (django 1.1.1, haven't check with another version) put that in settings because importing signals there will break things.
A better choice would be to put it in a dummy app's models module, and to put that app on top of the INSTALLED_APPS list/tuple (so it gets imported before anything else). Here is an example of what you can have in myhackishfix_app/models.py :
from django.db.models.signals import class_prepared
def longer_username(sender, *args, **kwargs):
# You can't just do `if sender == django.contrib.auth.models.User`
# because you would have to import the model
# You have to test using __name__ and __module__
if sender.__name__ == "User" and sender.__module__ == "django.contrib.auth.models":
sender._meta.get_field("username").max_length = 75
class_prepared.connect(longer_username)
That will do the trick.
A few notes though:
You might want to change also the help_text of the field, to reflect the new maximum length
If you want to use the automatic admin, you will have to subclass UserChangeForm, UserCreationForm and AuthenticationForm as the maximum length is not deduced from the model field, but directly in the form field declaration.
If you're using South, you can create the following migration to change the column in the underlying database:
import datetime
from south.db import db
from south.v2 import SchemaMigration
from django.db import models
class Migration(SchemaMigration):
def forwards(self, orm):
# Changing field 'User.username'
db.alter_column('auth_user', 'username', models.CharField(max_length=75))
def backwards(self, orm):
# Changing field 'User.username'
db.alter_column('auth_user', 'username', models.CharField(max_length=35))
models = {
# ... Copy the remainder of the file from the previous migration, being sure
# to change the value for auth.user / usename / maxlength
Based on Clément and Matt Miller's great combined answer above, I've pulled together a quick app that implements it. Pip install, migrate, and go. Would put this as a comment, but don't have the cred yet!
https://github.com/GoodCloud/django-longer-username
EDIT 2014-12-08
The above module is now deprecated in favor of https://github.com/madssj/django-longer-username-and-email
Updated solution for the Django 1.3 version (without modifying manage.py):
Create new django-app:
monkey_patch/
__init__.py
models.py
Install it as first: (settings.py)
INSTALLED_APPS = (
'monkey_patch',
#...
)
Here is models.py:
from django.contrib.auth.models import User
from django.core.validators import MaxLengthValidator
NEW_USERNAME_LENGTH = 300
def monkey_patch_username():
username = User._meta.get_field("username")
username.max_length = NEW_USERNAME_LENGTH
for v in username.validators:
if isinstance(v, MaxLengthValidator):
v.limit_value = NEW_USERNAME_LENGTH
monkey_patch_username()
The solutions above do seem to update the model length. However, to reflect your custom length in admin, you also need to override the admin forms (frustratingly, they don't simply inherit the length from the model).
from django.contrib.auth.forms import UserChangeForm, UserCreationForm
UserChangeForm.base_fields['username'].max_length = NEW_USERNAME_LENGTH
UserChangeForm.base_fields['username'].widget.attrs['maxlength'] = NEW_USERNAME_LENGTH
UserChangeForm.base_fields['username'].validators[0].limit_value = NEW_USERNAME_LENGTH
UserChangeForm.base_fields['username'].help_text = UserChangeForm.base_fields['username'].help_text.replace('30', str(NEW_USERNAME_LENGTH))
UserCreationForm.base_fields['username'].max_length = NEW_USERNAME_LENGTH
UserCreationForm.base_fields['username'].widget.attrs['maxlength'] = NEW_USERNAME_LENGTH
UserCreationForm.base_fields['username'].validators[0].limit_value = NEW_USERNAME_LENGTH
UserCreationForm.base_fields['username'].help_text = UserChangeForm.base_fields['username'].help_text.replace('30', str(NEW_USERNAME_LENGTH))
As far as I know one can override user model since Django 1.5 which will solve a problem. Simple example here
If you simply modify the database table, you'll still have to deal with Django's validation, so it won't let you make one over 30 characters anyways. Additionally, the username validates so that it can't have special characters like # so simply modifying the length of the field wouldn't work anyways. My bad, looks like it handles that. Here's the username field from models.py in django.contrib.auth:
username = models.CharField(_('username'), max_length=30, unique=True, help_text=_("Required. 30 characters or fewer. Letters, numbers and #/./+/-/_ characters"))
Creating email auth is not hard. Here's a super simple email auth backend you can use. Al l you need to do after that is add some validation to ensure the email address is unique and you're done. That easy.
Yes, it can be done. At least I think this should work; I wound up replacing the whole auth model, so am ready to be corrected if this doesn't work out...
If you have no user records you care about:
drop the auth_user table
change username to max_length=75 in the model
syncdb
If you have user records you need to retain then it's more complicated as you need to migrate them somehow. Easiest is backup and restore of the data from old to new table, something like:
backup the user table data
drop the table
syncdb
reimport user data to the new table; taking care to restore the original id values
Alternatively, using your mad python-django skillz, copy the user model instances from old to new and replace:
create your custom model and temporarily stand it alongside the default model
write a script which copies the instances from the default model to the new model
replace the default model with your custom one
The latter is not as hard as it sounds, but obviously involves a bit more work.
Fundamentally, the problem is that some people want to use an email address as the unique identifier, while the user authentication system in Django requires a unique username of at most 30 characters. Perhaps that will change in the future, but that's the case with Django 1.3 as I'm writing.
We know that 30 characters is too short for many email addresses; even 75 characters is not enough to represent some email addresses, as explained in What is the optimal length for an email address in a database?.
I like simple solutions, so I recommend hashing the email address into a username that fits the restrictions for usernames in Django. According to User authentication in Django, a username must be at most 30 characters, consisting of alphanumeric characters and _, #, +, . and -. Thus, if we use base-64 encoding with careful substitution of the special characters, we have up to 180 bits. So we can use a 160-bit hash function like SHA-1 as follows:
import hashlib
import base64
def hash_user(email_address):
"""Create a username from an email address"""
hash = hashlib.sha1(email_address).digest()
return base64.b64encode(hash, '_.').replace('=', '')
In short, this function associates a username for any email address. I'm aware that there is a tiny probability of a collision in the hash function, but this should not be an issue in most applications.
Just adding the below code at the bottom of settings.py
from django.contrib.auth.models import User
User._meta.get_field("username").max_length = 75
C:...\venv\Lib\site-packages\django\contrib\auth\models.py
first_name = models.CharField(_('first name'), max_length=30, blank=True)
change to
first_name = models.CharField(_('first name'), max_length=75, blank=True)
save
and change in the database
I am using django 1.4.3 which makes it pretty easy and I did not have to change anything else in my code after realising I wanted to use long email addresses as usernames.
If you have direct access to the database, change it there to the amount of characters you would like to, in my case 100 characters.
In your app model (myapp/models.py) add the following
from django.contrib.auth.models import User
class UserProfile(models.Model):
# This field is required.
User._meta.get_field("username").max_length = 100
user = models.OneToOneField(User)
Then in your settings.py you specify the model:
AUTH_USER_MODEL = 'myapp.UserProfile'
If you are using venv (virtual environment), the simplest solution probably is just update the core code directly, i.e. opening the following two files:
- - venv/lib/python2.7/sites-packages/django/contrib/auth/model.py
- venv/lib/python2.7/sites-packages/django/contrib/auth/forms.py
Search for all username field and change max_length from 30 to 100. It is safe since you are already using venv so it won't affect any other Django project.
The best solution is to use email field for email and the username for username.
In the input login form validation, find whether the data is username or the email and if email, query the email field.
This only requires monkey patching the contrib.auth.forms.login_form which is a few lines in the corresponding view.
And it is far better than trying to modify the models and the database tables.
I'm trying to learn Django and I would like feedback from anyone who has any MVC/MTV/PHP/Ruby framework experience. Does anyone find that the user model is too tightly coupled with auth?
Background: When you first implement authentication for Django, you include the module django.contrib.auth
This will bring in several models like User, Group, Message etc. Let's focus on the User model as this is the one of the most important tables in any website.
In short the User table has these fields
User
username max_length 30, unique, [letters, digits, underscores]
password max_length 75
email max_length 75
...and about 8 other useful fields like first_name, last_name, etc.
Goal:
I want to remove username and use email as the login for every user. It's a pretty simple request that many websites use these days.
I don't want to monkey patch the core code since this will make upgrading more difficult later on. This means modifying the User model is out of the question. I only want to do a few simple and basic things I expect a few frameworks to do so let me address how Django does it.
Adding new fields to the User model
Django docs says to use create another table and insert the fields there. You will have a one to one relationship between the User table and the Profile table.
eg.
If You want to add an image field to each user you add it to the profile table. A join query is made every single time. They've even specified a constant to tell the framework what table to use:
AUTH_PROFILE_MODULE = 'accounts.UserProfile'
I don't think it's the best practice to have to do a join query every time I want a field that should belong to the user table.
Another option is to use the function add_to_class.
The django community has stated it's not good to define new fields outside of the main class because other developers who add methods won't know all the data members.
Editing old fields
The auth module does a check against two fields username and the hashed password. Looking at the above table I would need to change the username model to accept these properties. Length of 75 with all the valid characters of the email. The django suggests I check against the email field.
Two problems arise if I use the email field to auth against:
I need to write a new class to be used in a constant AUTHENTICATION_BACKEND, so it checks against the email field and I have an unused field called username.
Adding new methods
In MVC/MTV a design principle is to use fat models skinny controllers. Since the model is declared in auth, I'm not sure how one is supposed to add methods that act on the user model's fields. Since django suggests using a Profile model, I suppose they will have to go there.
Extending the User class
A small annoyance would be that I can't use the name 'User' and instead must use 'Users' or 'Accounts'. A bigger one is I don't think the auth would recognize this new module. Meaning I would have to rewrite a bunch functionality that is is present. This one doesn't bother me as it's something I expect to do in other frameworks.
Any comments are appreciated. I wouldn't ask all these questions and look for solutions if I wasn't truly interested in using django.
I agree that django's incessant clinginess to the auth models is absurd. My job requires me to create ultra scalable and very high load sites which sometimes require user authentication and djano's auth model + permissions does not fit with that.
Fortunately, it's not difficult to replace.
First, create a custom User model.
class User(models.Model):
...fields...
#Define some interface methods to be compatible.
def get_and_delete_messages(self):
def is_active(self):
def is_anonymous(self):
def is_authenticated(self):
def is_staff(self):
def has_perm(self, perm_list):
Second, create your own authentication back-end.
class LocalAccount(object):
"""
This checks our local user DB for authentication
"""
def authenticate(self, username=None, password=None):
try:
user = User.objects.get(alias=username)
if user.check_password(password):
return user
except User.DoesNotExist:
return None
def get_user(self, user_id):
try:
return User.objects.select_related().get(pk=user_id)
except User.DoesNotExist:
return None
#settings.py
AUTHENTICATION_BACKENDS = (
'helpers.auth.LocalAccount',
)
That should solve most of your issues, I don't even think all of the methods you would find on django.contrib.auth.User are necessary, I recommend trying it out.
The one gotcha here is that the admin may start to bitch, fortunately that's really easy to patch using simple python inheritance as well. That's another question though :)
At the end of the day your project's auth backend needs some sort of store for auth credentials. That the default auth backend is tightly coupled to the User model is not strange in this respect. It's easy enough to substitute your own definition for the user model if you write your own auth backend, as I have in the past.
I created my Profile model and use AUTH_PROFILE_MODULE, so I have complete control over my model, I can modify fields, add methods, etc. Now I'm thinking about using cache and writing middleware that will get profile from cache if possible.
To login using email you could write very simple auth backend:
from django.contrib.auth.models import User
from django.contrib.auth.backends import ModelBackend
class EmailModelBackend(ModelBackend):
def authenticate(self, username=None, password=None):
try:
user = User.objects.get(email=username)
if user.check_password(password):
return user
except User.DoesNotExist:
return None
I need to patch the standard User model of contrib.auth by ensuring the email field entry is unique:
User._meta.fields[4].unique = True
Where is best place in code to do that?
I want to avoid using the number fields[4]. It's better to user fields['email'], but fields is not dictionary, only list.
Another idea may be to open a new ticket and upload a patch with new parameter inside settings.py:
AUTH_USER_EMAIL_UNIQUE = True
Any suggestions on the most correct way to achieve email address uniqueness in the Django User model?
Caution:
The code below was written for an older version of Django (before Custom
User Models were introduced). It contains a race condition, and
should only be used with a Transaction Isolation Level of SERIALIZABLE
and request-scoped transactions.
Your code won't work, as the attributes of field instances are read-only. I fear it might be a wee bit more complicated than you're thinking.
If you'll only ever create User instances with a form, you can define a custom ModelForm that enforces this behavior:
from django import forms
from django.contrib.auth.models import User
class UserForm(forms.ModelForm):
class Meta:
model = User
def clean_email(self):
email = self.cleaned_data.get('email')
username = self.cleaned_data.get('username')
if email and User.objects.filter(email=email).exclude(username=username).exists():
raise forms.ValidationError(u'Email addresses must be unique.')
return email
Then just use this form wherever you need to create a new user.
BTW, you can use Model._meta.get_field('field_name') to get fields by name, rather than by position. So for example:
# The following lines are equivalent
User._meta.fields[4]
User._meta.get_field('email')
UPDATE
The Django documentation recommends you use the clean method for all validation that spans multiple form fields, because it's called after all the <FIELD>.clean and <FIELD>_clean methods. This means that you can (mostly) rely on the field's value being present in cleaned_data from within clean.
Since the form fields are validated in the order they're declared, I think it's okay to occasionally place multi-field validation in a <FIELD>_clean method, so long as the field in question appears after all other fields it depends on. I do this so any validation errors are associated with the field itself, rather than with the form.
What about using unique_together in a "different" way? So far it works for me.
class User(AbstractUser):
...
class Meta(object):
unique_together = ('email',)
Simply use below code in models.py of any app
from django.contrib.auth.models import User
User._meta.get_field('email')._unique = True
In settings module:
# Fix: username length is too small,email must be unique
from django.contrib.auth.models import User, models
User._meta.local_fields[1].__dict__['max_length'] = 75
User._meta.local_fields[4].__dict__['_unique'] = True
It's amazing, but I found a best solution for me!
django-registration have form with checking uniqueness of email field: RegistrationFormUniqueEmail
example of usage here
Your form should look something like this.
def clean_email(self):
email = self.cleaned_data.get('email')
username = self.cleaned_data.get('username')
print User.objects.filter(email=email).count()
if email and User.objects.filter(email=email).count() > 0:
raise forms.ValidationError(u'This email address is already registered.')
return email
To ensure a User, no matter where, be saved with a unique email, add this to your models:
#receiver(pre_save, sender=User)
def User_pre_save(sender, **kwargs):
email = kwargs['instance'].email
username = kwargs['instance'].username
if not email: raise ValidationError("email required")
if sender.objects.filter(email=email).exclude(username=username).count(): raise ValidationError("email needs to be unique")
Note that this ensures non-blank email too. However, this doesn't do forms validation as would be appropriated, just raises an exception.
Django has a Full Example on its documentation on how to substitute and use a Custom User Model, so you can add fields and use email as username.
One possible way to do this is to have a pre-save hook on the User object and reject the save of the email already exists in the table.
I think that the correct answer would assure that uniqueness check was placed inside the database (and not on the django side). Because due to timing and race conditions you might end with duplicate emails in the database despite having for example pre_save that does proper checks.
If you really need this badly I guess you might try following approach:
Copy User model to your own app, and change field email to be unique.
Register this user model in the admin app (using admin class from django.contrib.auth.admin)
Create your own authentication backend that uses your model instead of django one.
This method won't make email field unique at the database level, but it's worth trying.
Use a custom validator:
from django.core.exceptions import ValidationError
from django.contrib.auth.models import User
def validate_email_unique(value):
exists = User.objects.filter(email=value)
if exists:
raise ValidationError("Email address %s already exists, must be unique" % value)
Then in forms.py:
from django.contrib.auth.models import User
from django.forms import ModelForm
from main.validators import validate_email_unique
class UserForm(ModelForm):
#....
email = forms.CharField(required=True, validators=[validate_email_unique])
#....
Add the below function in any of the models.py file. Then run makemigrations and migrate. Tested on Django1.7
def set_email_as_unique():
"""
Sets the email field as unique=True in auth.User Model
"""
email_field = dict([(field.name, field) for field in MyUser._meta.fields])["email"]
setattr(email_field, '_unique', True)
#this is called here so that attribute can be set at the application load time
set_email_as_unique()
Since version 1.2 (May 11th, 2015) there has been a way to dynamically import any chosen registration form using the settings option REGISTRATION_FORM.
So, one could use something like this:
REGISTRATION_FORM = 'registration.forms.RegistrationFormUniqueEmail'
This is documented here.
And here's the link to the changelog entry.
Django does not allow direct editing User object but you can add pre_save signal and achieve unique email. for create signals u can follow https://docs.djangoproject.com/en/2.0/ref/signals/. then add the following to your signals.py
#receiver(pre_save, sender=User)
def check_email(sender,instance,**kwargs):
try:
usr = User.objects.get(email=instance.email)
if usr.username == instance.username:
pass
else:
raise Exception('EmailExists')
except User.DoesNotExist:
pass
Add somewhere this:
User._meta.get_field_by_name('email')[0]._unique = True
and then execute SQL similar to this:
ALTER TABLE auth_user ADD UNIQUE (email);
The first answer here is working for me when I'm creating new users, but it fails when I try to edit a user, since I am excluding the username from the view. Is there a simple edit for this that will make the check independent of the username field?
I also tried including the username field as a hidden field (since I don't want people to edit it), but that failed too because django was checking for duplicate usernames in the system.
(sorry this is posted as an answer, but I lack the creds to post it as a comment. Not sure I understand Stackoverflow's logic on that.)
You can use your own custom user model for this purpose. You can use email as username or phone as username , can have more than one attribute.
In your settings.py you need to specify below settings
AUTH_USER_MODEL = 'myapp.MyUser'.
Here is the link that can help you .
https://docs.djangoproject.com/en/1.8/topics/auth/customizing/#auth-custom-user
from an User inherited model, redefine the attribute correctly. It should work, as is it's not usefull to have that in django core because it's simple to do.
I went to \Lib\site-packages\django\contrib\auth\models
and in class AbstractUser(AbstractBaseUser, PermissionsMixin):
I changed email to be:
email = models.EmailField(_('email address'), **unique=True**, blank=True)
With this if you try to register with email address already present in the database you will get message: User with this Email address already exists.