class LoginForm(forms.ModelForm):
	password = forms.CharField(widget = forms.PasswordInput(), label = 'Your Password')
	class Meta:
		model = User
		fields = ('username', 'password')

class WelcomeView(View):
	http_method_names = ['get','post']
	def get(self, request):
		template_name = 'Welcome.html'
		form = LoginForm()
		return render(request,template_name,{'form':form})
	def post(self, request):
		logout(request)
		form = LoginForm(request.POST)
		if form.is_valid():
			username = form.cleaned_data['username']
			password = form.cleaned_data['password']
			user = authenticate(username = username, password = password)
			if user is not None:
				if user.is_active:
					login(request,user)
					return redirect('schedule')
				else:
					print('User is inactive')
			else:
				print('Invalid login')
				print(form.errors)
		else:
			print('Not valid!', form.errors)
			form = LoginForm()
		return reverse('welcome')

<p>Please, login to proceed...</p>
	{% if form.errors %}
	<p> Your username and password didn't math</p>
	{% endif %}
	<form name = "LoginForm"action = "{{action}}" method="post">
		{% csrf_token %}
  		{% if form.non_field_errors %}
		<div class="form_errors">
  		{% for err in form.non_field_errors %}
  		<div class="form_error_message">{{ err }}</div>
  		{% endfor %}
		</div>	
		{% endif %}
		{% for hidden in form.hidden_fields %}
   		{{ hidden }}
		{% endfor %}
		{% for field in form.visible_fields %}
 		<div {% if field.errors %}class="field_error"{% endif %}>
    	{{ field.label_tag }}
    	{{ field }}
    	{% for err in field.errors %}
    	<span class="error_message">{{ err }}</span>
    	{% endfor %}
  		</div>
		{% endfor %}
  		{% for i in form.errors %}
  			{{ i }}
  		{% endfor %}
  		<input type="submit" value = "login">
	</form>

return render(request,template_name,{'form':form})

form = LoginForm(request.POST)
if form.is_valid():
    ...
    return reverse('welcome')
print('Not valid!', form.errors)
# form = LoginForm()  # Вот этого делать не надо, т.к. вы форму которая содержит ошибки затираете пустой формой
return render(request,template_name,{'form':form})

raise forms.ValidationError("This user is inactive!")

class LoginForm(forms.Form):
	username = forms.CharField(label = 'Your Name')
	password = forms.CharField(widget = forms.PasswordInput(), label = 'Your Password')
	def clean_username(self):
		username = self.cleaned_data['username']
		try:
			user = User.objects.get(username = username)
			if not user.is_active:
				raise forms.ValidationError("User is inactive!")
			else:
				return username
		except User.DoesNotExist:
			raise forms.ValidationError("User not Exist!")

class WelcomeView(View):
	http_method_names = ['get','post']
	def get(self, request):
		template_name = 'Welcome.html'
		form = LoginForm()
		print(form.errors)
		return render(request,template_name,{'form':form})
	
	def post(self, request):
		logout(request)
		template_name = 'Welcome.html'
		form = LoginForm(request.POST)
		if form.is_valid():
			username = form.cleaned_data['username']
			password = form.cleaned_data['password']
			user = authenticate(username = username, password = password)
			if user is not None:
				if user.is_active:
					login(request,user)
					return redirect('schedule')
				else:
					print('User is inactive')
					
			else:
				print('Invalid login')
				print(form.errors)
		else:
			print('Not valid!', form.errors)
		return render(request, template_name,{'form':form})

return render(request, template_name,{'form':form})

# views.py
from django.contrib.auth import views as auth_views
   
def login_view(request):
    if request.user.is_authenticated():
        return HttpResponseRedirect('/')
    return auth_views.login(request, template_name='profiles/login.html')
    
# urls.py
...
url(r'^login/$', login_view, name='login'),
...