{{ hint }}
返回登录 ``` 注意，在上面的表单中，我们使用了模板指令`{% csrf_token %}`为表单添加一个隐藏域（type属性值为hidden的input标签），它的作用是在表单中生成一个随机令牌（token）来防范[跨站请求伪造]({{ hint }}
注册新用户 ``` 上面的登录页中，我们要求用户提供验证码，验证码全称是**全自动区分计算机和人类的公开图灵测试**，它是一种用来区分系统的使用者是计算机还是人类的程序。简单的说就是程序出一个只有人类能够回答的问题，由系统使用者来解答，由于计算机理论上无法解答程序提出的问题，所以回答出问题的用户就可以被认为是人类。大多数的网站都使用了不同类型的验证码技术来防范用程序自动注册用户或模拟用户登录（暴力破解用户密码），因为验证码具有一次消费性，而没有通过图灵测试的程序是不能够完成注册或登录的。 在Python程序中生成验证码并不算特别复杂，但需要三方库Pillow的支持（PIL的分支），因为要对验证码图片进行旋转、扭曲、拉伸以及加入干扰信息来防范那些用OCR（光学文字识别）破解验证码的程序。下面的代码封装了生成验证码图片的功能，大家可以直接用这些代码来生成图片验证码，不要“重复发明轮子”。 ```Python """ 图片验证码 """ import os import random from io import BytesIO from PIL import Image from PIL import ImageFilter from PIL.ImageDraw import Draw from PIL.ImageFont import truetype class Bezier(object): """贝塞尔曲线""" def __init__(self): self.tsequence = tuple([t / 20.0 for t in range(21)]) self.beziers = {} def make_bezier(self, n): """绘制贝塞尔曲线""" try: return self.beziers[n] except KeyError: combinations = pascal_row(n - 1) result = [] for t in self.tsequence: tpowers = (t ** i for i in range(n)) upowers = ((1 - t) ** i for i in range(n - 1, -1, -1)) coefs = [c * a * b for c, a, b in zip(combinations, tpowers, upowers)] result.append(coefs) self.beziers[n] = result return result class Captcha(object): """验证码""" def __init__(self, width, height, fonts=None, color=None): self._image = None self._fonts = fonts if fonts else \ [os.path.join(os.path.dirname(__file__), 'fonts', font) for font in ['ArialRB.ttf', 'ArialNI.ttf', 'Georgia.ttf', 'Kongxin.ttf']] self._color = color if color else random_color(0, 200, random.randint(220, 255)) self._width, self._height = width, height @classmethod def instance(cls, width=200, height=75): prop_name = f'_instance_{width}_{height}' if not hasattr(cls, prop_name): setattr(cls, prop_name, cls(width, height)) return getattr(cls, prop_name) def background(self): """绘制背景""" Draw(self._image).rectangle([(0, 0), self._image.size], fill=random_color(230, 255)) def smooth(self): """平滑图像""" return self._image.filter(ImageFilter.SMOOTH) def curve(self, width=4, number=6, color=None): """绘制曲线""" dx, height = self._image.size dx /= number path = [(dx * i, random.randint(0, height)) for i in range(1, number)] bcoefs = Bezier().make_bezier(number - 1) points = [] for coefs in bcoefs: points.append(tuple(sum([coef * p for coef, p in zip(coefs, ps)]) for ps in zip(*path))) Draw(self._image).line(points, fill=color if color else self._color, width=width) def noise(self, number=50, level=2, color=None): """绘制扰码""" width, height = self._image.size dx, dy = width / 10, height / 10 width, height = width - dx, height - dy draw = Draw(self._image) for i in range(number): x = int(random.uniform(dx, width)) y = int(random.uniform(dy, height)) draw.line(((x, y), (x + level, y)), fill=color if color else self._color, width=level) def text(self, captcha_text, fonts, font_sizes=None, drawings=None, squeeze_factor=0.75, color=None): """绘制文本""" color = color if color else self._color fonts = tuple([truetype(name, size) for name in fonts for size in font_sizes or (65, 70, 75)]) draw = Draw(self._image) char_images = [] for c in captcha_text: font = random.choice(fonts) c_width, c_height = draw.textsize(c, font=font) char_image = Image.new('RGB', (c_width, c_height), (0, 0, 0)) char_draw = Draw(char_image) char_draw.text((0, 0), c, font=font, fill=color) char_image = char_image.crop(char_image.getbbox()) for drawing in drawings: d = getattr(self, drawing) char_image = d(char_image) char_images.append(char_image) width, height = self._image.size offset = int((width - sum(int(i.size[0] * squeeze_factor) for i in char_images[:-1]) - char_images[-1].size[0]) / 2) for char_image in char_images: c_width, c_height = char_image.size mask = char_image.convert('L').point(lambda i: i * 1.97) self._image.paste(char_image, (offset, int((height - c_height) / 2)), mask) offset += int(c_width * squeeze_factor) @staticmethod def warp(image, dx_factor=0.3, dy_factor=0.3): """图像扭曲""" width, height = image.size dx = width * dx_factor dy = height * dy_factor x1 = int(random.uniform(-dx, dx)) y1 = int(random.uniform(-dy, dy)) x2 = int(random.uniform(-dx, dx)) y2 = int(random.uniform(-dy, dy)) warp_image = Image.new( 'RGB', (width + abs(x1) + abs(x2), height + abs(y1) + abs(y2))) warp_image.paste(image, (abs(x1), abs(y1))) width2, height2 = warp_image.size return warp_image.transform( (width, height), Image.QUAD, (x1, y1, -x1, height2 - y2, width2 + x2, height2 + y2, width2 - x2, -y1)) @staticmethod def offset(image, dx_factor=0.1, dy_factor=0.2): """图像偏移""" width, height = image.size dx = int(random.random() * width * dx_factor) dy = int(random.random() * height * dy_factor) offset_image = Image.new('RGB', (width + dx, height + dy)) offset_image.paste(image, (dx, dy)) return offset_image @staticmethod def rotate(image, angle=25): """图像旋转""" return image.rotate(random.uniform(-angle, angle), Image.BILINEAR, expand=1) def generate(self, captcha_text='', fmt='PNG'): """生成验证码(文字和图片)""" self._image = Image.new('RGB', (self._width, self._height), (255, 255, 255)) self.background() self.text(captcha_text, self._fonts, drawings=['warp', 'rotate', 'offset']) self.curve() self.noise() self.smooth() image_bytes = BytesIO() self._image.save(image_bytes, format=fmt) return image_bytes.getvalue() def pascal_row(n=0): """生成Pascal三角第n行""" result = [1] x, numerator = 1, n for denominator in range(1, n // 2 + 1): x *= numerator x /= denominator result.append(x) numerator -= 1 if n & 1 == 0: result.extend(reversed(result[:-1])) else: result.extend(reversed(result)) return result def random_color(start=0, end=255, opacity=255): """获得随机颜色""" red = random.randint(start, end) green = random.randint(start, end) blue = random.randint(start, end) if opacity is None: return red, green, blue return red, green, blue, opacity ``` > 说明：上面的代码在生成验证码图片时用到了三种字体文件，使用上面的代码时需要添加字体文件到应用目录下的fonts目录中。 下面的视图函数用来生成验证码并通过HttpResponse对象输出到用户浏览器中。 ```Python ALL_CHARS = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' def get_captcha_text(length=4): selected_chars = random.choices(ALL_CHARS, k=length) return ''.join(selected_chars) def get_captcha(request): """获得验证码""" captcha_text = get_captcha_text() image = Captcha.instance().generate(captcha_text) return HttpResponse(image, content_type='image/png') ``` 生成的验证码如下图所示。  为了验证用户提交的登录表单，我们再定义个表单类。 ```Python class LoginForm(forms.Form): username = forms.CharField(min_length=4, max_length=20) password = forms.CharField(min_length=8, max_length=20) captcha = forms.CharField(min_length=4, max_length=4) def clean_username(self): username = self.cleaned_data['username'] if not USERNAME_PATTERN.fullmatch(username): raise ValidationError('无效的用户名') return username def clean_password(self): return to_md5_hex(self.cleaned_data['password']) ``` 跟之前我们定义的注册表单类略有区别，登录表单类直接继承自Form没有跟模型绑定，定义了三个字段分别对应登录表单中的用户名、密码和验证码。接下来是处理用户登录的视图函数。 ```Python def login(request): hint = '' if request.method == 'POST': form = LoginForm(request.POST) if form.is_valid(): username = form.cleaned_data['username'] password = form.cleaned_data['password'] user = User.objects.filter(username=username, password=password).first() if user: return redirect('/') else: hint = '用户名或密码错误' else: hint = '请输入有效的登录信息' return render(request, 'login.html', {'hint': hint}) ``` 映射URL。 ```Python from django.contrib import admin from django.urls import path from vote import views urlpatterns = [ # 此处省略上面的代码 path('login/', views.login, name='login'), # 此处省略下面的代码 ] ``` 需要指出，上面我们设定用户登录成功时直接返回首页，而且在用户登录时并没有验证用户输入的验证码是否正确，这些我们留到下一个单元再为大家讲解。另外，如果要在Django自带的管理后台中进行表单验证，可以在admin.py的模型管理类中指定`form`属性为自定义的表单即可，例如： ```Python class UserForm(forms.ModelForm): password = forms.CharField(min_length=8, max_length=20, widget=forms.PasswordInput, label='密码') def clean_username(self): username = self.cleaned_data['username'] if not USERNAME_PATTERN.fullmatch(username): raise ValidationError('用户名由字母、数字和下划线构成且长度为4-20个字符') return username def clean_password(self): password = self.cleaned_data['password'] return to_md5_hex(self.cleaned_data['password']) class Meta: model = User exclude = ('no', ) class UserAdmin(admin.ModelAdmin): list_display = ('no', 'username', 'password', 'email', 'tel') ordering = ('no', ) form = UserForm list_per_page = 10 admin.site.register(User, UserAdmin) ```