Widget Select in Django does not appear in form

My signup page is not showing up the selection fields, my code is as follows:

forms.py

class InscricaoForm(forms.Form):

    VINCULO = [
        (u'b', u'Bolsista'),
        (u'e', u'Estagiário'),
        (u't', u'Terceiro'),
        (u's', u'Servidor'),
    ]

    SALAS = [
        (u'1', u'SysAdmin'),
        (u'2', u'Help Desk'),
    ]
    vinculo = forms.ChoiceField(choices=(VINCULO), label='Vinculo')
    registro = forms.IntegerField(label=_('Registro'))
    nome = forms.CharField(label=_('Nome'))
    email_inpe = forms.EmailField(label=_('Email @ Inpe'))
    email = forms.EmailField(label=_('Email'))
    data_admissao = forms.DateField(label=_('Data de Admissao'))

    sala = forms.CharField(widget=forms.Select(choices=SALAS),label=_('Salas'))

    ramal = forms.CharField(label=_('Ramal'))


class Bolsista_EstagiarioForm(InscricaoForm):
    data_fim_contrato = forms.DateField(label=_('Data de Fim de Contrato'))

class TerceiroForm(InscricaoForm):
    empresa = forms.CharField(label=_('Empresa'))

class ServidorForm(InscricaoForm):
    tipo = forms.CharField(label=_('Tipo de Servidor'))


class InscricaoForm(forms.ModelForm):
        class Meta:
            model = Inscricao
            fields = '__all__'

models.py

VINCULO = (
    (u'b', u'Bolsista'),
    (u'e', u'Estagiário'),
    (u't', u'Terceiro'),
    (u's', u'Servidor'),
    )

SALAS = (
    (u'1', u'SysAdmin'),
    (u'2', u'Help Desk'),
)

EMPRESAS = (
    (u'1', u'Cray'),
    (u'2', u'Outros'),
)

SERVIDOR = (
    (u'1', u'Técnico'),
    (u'2', u'Tecnologista'),
)


class Inscricao(models.Model):

    # criando relacionamento 1:1 com o user do django
        usuario = models.OneToOneField(User)
        vinculo = models.CharField(max_length=100, choices=VINCULO)
        registro = models.IntegerField()
        email_inpe = models.EmailField(blank=True)
        data_admissao = models.DateField()
        sala = models.CharField(max_length=100, choices=SALAS)
        ramal = models.CharField(max_length=30)
        criado_em = models.DateTimeField('criado em', auto_now_add=True)

        class Meta:
                abstract = True

class Bolsista_Estagiario(Inscricao):
    data_fim_contrato = models.DateField()

    class Meta:
        verbose_name_plural = "Bolsistas e Estagiários"


class Terceiro(Inscricao):
    empresa = models.CharField(max_length=30, choices=EMPRESAS)

    class Meta:
        verbose_name_plural = "Terceiros"

class Servidor(Inscricao):
    tipo = models.CharField(max_length=30, choices=SERVIDOR)

    class Meta:
        verbose_name_plural = "Servidores"

views.py

def inscricao(request):
    form_class = InscricaoForm

    # new logic!
    if request.method == 'POST':
        form = form_class(data=request.POST)

        if form.is_valid():
            vinculo= request.POST.get(
                'vinculo'
            , '')
            registro= request.POST.get(
                'registro'
            , '')
            nome = request.POST.get(
                'nome'
            , '')
            email_inpe= request.POST.get(
                'email_inpe'
            , '')
            email= request.POST.get(
                'email'
            , '')
            data_admissao= request.POST.get(
                'data_admissao'
            , '')


            form_content = request.POST.get('content', '')

            # Email the profile with the
            # contact information
            template = get_template('contact_template.txt')


            content = template.render({'vinculo': vinculo,'registro': registro,
                                              'nome': nome,'email_inpe': email_inpe,
                                              'email': email,'data_admissao': data_admissao,'form_content': form_content})

            email = EmailMessage(
                "Novo usuário cadastrado",
                content,
                "Portal Cptec" +'',
                ['[email protected]'],
                headers = {'Reply-To': '[email protected]' }
            )
            email.send()

            messages.success(request, 'Profile details updated.')

admin.py

class InscricaoAdmin(UserAdmin):

    add_fieldsets = (
        (None, {
            'classes': ('wide',),
            'fields': ('username', 'email', 'first_name', 'last_name', 'password1', 'password2'),
        }),
    )


admin.site.register(Bolsista_Estagiario)
admin.site.register(Servidor)
admin.site.register(Terceiro)
#admin.site.register(Inscricao)
admin.site.unregister(User)

admin.site.register(User, InscricaoAdmin)