雖然表單字段的Field類主要使用在Form類中，但也能夠直接實例化它們來使用，以便更好地瞭解它們是如何工做的。每一個Field的實例都有一個clean()方法，它接受一個參數，而後返回「清潔的」數據或者拋出一個django.forms.ValidationError異常：前端
>>> from django import forms >>> f = forms.EmailField() >>> f.clean('foo@example.com') 'foo@example.com' >>> f.clean('invalid email address') Traceback (most recent call last): ... ValidationError: ['Enter a valid email address.']
這個clean方法常常被咱們用來在開發或測試過程當中對數據進行驗證和測試。git
如下的參數是每一個Field類均可以使用的。web
給字段添加必填屬性，不能空着。正則表達式
>>> from django import forms >>> f = forms.CharField() >>> f.clean('foo') 'foo' >>> f.clean('') Traceback (most recent call last): ... ValidationError: ['This field is required.'] >>> f.clean(None) Traceback (most recent call last): ... ValidationError: ['This field is required.'] >>> f.clean(' ') ' ' >>> f.clean(0) '0' >>> f.clean(True) 'True' >>> f.clean(False) 'False'
若要表示一個字段不是必需的，設置required=False：django
>>> f = forms.CharField(required=False)
>>> f.clean('foo')
'foo'
>>> f.clean('')
''
>>> f.clean(None)
''
>>> f.clean(0)
'0'
>>> f.clean(True)
'True'
>>> f.clean(False)
'False'
label參數用來給字段添加‘人類友好’的提示信息。若是沒有設置這個參數，那麼就用字段的首字母大寫名字。好比：服務器
下面的例子，前兩個字段有，最後的comment沒有label參數：函數
>>> from django import forms >>> class CommentForm(forms.Form): ... name = forms.CharField(label='Your name') ... url = forms.URLField(label='Your website', required=False) ... comment = forms.CharField() >>> f = CommentForm(auto_id=False) >>> print(f) <tr><th>Your name:</th><td><input type="text" name="name" required /></td></tr> <tr><th>Your website:</th><td><input type="url" name="url" /></td></tr> <tr><th>Comment:</th><td><input type="text" name="comment" required /></td></tr>
Django默認爲上面的label參數後面加個冒號後綴，若是想自定義，可使用label_suffix參數。好比下面的例子用「？」代替了冒號：測試
>>> class ContactForm(forms.Form):
... age = forms.IntegerField()
... nationality = forms.CharField()
... captcha_answer = forms.IntegerField(label='2 + 2', label_suffix=' =')
>>> f = ContactForm(label_suffix='?')
>>> print(f.as_p())
<p><label for="id_age">Age?</label> <input id="id_age" name="age" type="number" required /></p> <p><label for="id_nationality">Nationality?</label> <input id="id_nationality" name="nationality" type="text" required /></p> <p><label for="id_captcha_answer">2 + 2 =</label> <input id="id_captcha_answer" name="captcha_answer" type="number" required /></p>
爲HTML頁面中表單元素定義初始值。也就是input元素的value參數的值，以下所示：ui
>>> from django import forms >>> class CommentForm(forms.Form): ... name = forms.CharField(initial='Your name') ... url = forms.URLField(initial='http://') ... comment = forms.CharField() >>> f = CommentForm(auto_id=False) >>> print(f) <tr><th>Name:</th><td><input type="text" name="name" value="Your name" required /></td></tr> <tr><th>Url:</th><td><input type="url" name="url" value="http://" required /></td></tr> <tr><th>Comment:</th><td><input type="text" name="comment" required /></td></tr>
你可能會問爲何不在渲染表單的時候傳遞一個包含初始化值的字典給它，不是更方便？由於若是這麼作，你將觸發表單的驗證過程，此時輸出的HTML頁面將包含驗證中產生的錯誤，以下所示：this
>>> class CommentForm(forms.Form):
... name = forms.CharField()
... url = forms.URLField()
... comment = forms.CharField()
>>> default_data = {'name': 'Your name', 'url': 'http://'}
>>> f = CommentForm(default_data, auto_id=False)
>>> print(f)
<tr><th>Name:</th><td><input type="text" name="name" value="Your name" required /></td></tr> <tr><th>Url:</th><td><ul class="errorlist"><li>Enter a valid URL.</li></ul><input type="url" name="url" value="http://" required /></td></tr> <tr><th>Comment:</th><td><ul class="errorlist"><li>This field is required.</li></ul><input type="text" name="comment" required /></td></tr>
這就是爲何initial參數只用在未綁定的表單上。
還要注意，若是提交表單時某個字段的值沒有填寫，initial的值不會做爲「默認」的數據。initial值只用於原始表單的顯示：
>>> class CommentForm(forms.Form):
... name = forms.CharField(initial='Your name')
... url = forms.URLField(initial='http://')
... comment = forms.CharField()
>>> data = {'name': '', 'url': '', 'comment': 'Foo'}
>>> f = CommentForm(data)
>>> f.is_valid()
False
# The form does *not* fall back to using the initial values.
>>> f.errors
{'url': ['This field is required.'], 'name': ['This field is required.']}
除了常量以外，你還能夠傳遞一個可調用的對象：
>>> import datetime >>> class DateForm(forms.Form): ... day = forms.DateField(initial=datetime.date.today) >>> print(DateForm()) <tr><th>Day:</th><td><input type="text" name="day" value="12/23/2008" required /><td></tr>
最重要的參數之一，指定渲染Widget時使用的widget類，也就是這個form字段在HTML頁面中是顯示爲文本輸入框？密碼輸入框？單選按鈕？多選框？仍是別的....
該參數用於設置字段的輔助描述文本。
>>> from django import forms >>> class HelpTextContactForm(forms.Form): ... subject = forms.CharField(max_length=100, help_text='100 characters max.') ... message = forms.CharField() ... sender = forms.EmailField(help_text='A valid email address, please.') ... cc_myself = forms.BooleanField(required=False) >>> f = HelpTextContactForm(auto_id=False) >>> print(f.as_table()) <tr><th>Subject:</th><td><input type="text" name="subject" maxlength="100" required /><br /><span class="helptext">100 characters max.</span></td></tr> <tr><th>Message:</th><td><input type="text" name="message" required /></td></tr> <tr><th>Sender:</th><td><input type="email" name="sender" required /><br />A valid email address, please.</td></tr> <tr><th>Cc myself:</th><td><input type="checkbox" name="cc_myself" /></td></tr> >>> print(f.as_ul())) <li>Subject: <input type="text" name="subject" maxlength="100" required /> <span class="helptext">100 characters max.</span></li> <li>Message: <input type="text"