Once you have a Template object, you can render multiple contexts through it. For example:

>>> from django.template import Template, Context 
>>> t = Template('Hello, {{ name }}') 
>>> print (t.render(Context({'name': 'John'}))) 
Hello, John 
>>> print (t.render(Context({'name': 'Julie'}))) 
Hello, Julie 
>>> print (t.render(Context({'name': 'Pat'}))) 
Hello, Pat 

Whenever you're using the same template source to render multiple contexts like this, it's more efficient to create the Template object once, and then call render() on it multiple times:

# Bad 
for name in ('John', 'Julie', 'Pat'): 
    t = Template('Hello, {{ name }}') 
    print (t.render(Context({'name': name}))) 
 
# Good 
t = Template('Hello, {{ name }}') 
for name in ('John', 'Julie', 'Pat'): 
    print (t.render(Context({'name': name}))) 

Django's template parsing is quite fast. Behind the scenes, most of the parsing happens via a call to a single regular expression. This is in stark contrast to XML-based template engines, which incur the overhead of an XML parser and tend to be orders of magnitude slower than Django's template rendering engine.

In the examples so far, we've passed simple values in the contexts-mostly strings, plus a datetime.date example. However, the template system elegantly handles more complex data structures, such as lists, dictionaries, and custom objects. The key to traversing complex data structures in Django templates is the dot character (".").

Use a dot to access dictionary keys, attributes, methods, or indices of an object. This is best illustrated with a few examples. For instance, suppose you're passing a Python dictionary to a template. To access the values of that dictionary by dictionary key, use a dot:

>>> from django.template import Template, Context 
>>> person = {'name': 'Sally', 'age': '43'} 
>>> t = Template('{{ person.name }} is {{ person.age }} years old.') 
>>> c = Context({'person': person}) 
>>> t.render(c) 
'Sally is 43 years old.' 

Similarly, dots also allow access to object attributes. For example, a Python datetime.date object has year, month, and day attributes, and you can use a dot to access those attributes in a Django template:

>>> from django.template import Template, Context 
>>> import datetime 
>>> d = datetime.date(1993, 5, 2) 
>>> d.year 
1993 
>>> d.month 
5 
>>> d.day 
2 
>>> t = Template('The month is {{ date.month }} and the year is {{ date.year }}.') 
>>> c = Context({'date': d}) 
>>> t.render(c) 
'The month is 5 and the year is 1993.' 

This example uses a custom class, demonstrating that variable dots also allow attribute access on arbitrary objects:

>>> from django.template import Template, Context 
>>> class Person(object): 
...     def __init__(self, first_name, last_name): 
...         self.first_name, self.last_name = first_name, last_name 
>>> t = Template('Hello, {{ person.first_name }} {{ person.last_name }}.') 
>>> c = Context({'person': Person('John', 'Smith')}) 
>>> t.render(c) 
'Hello, John Smith.' 

Dots can also refer to methods of objects. For example, each Python string has the methods upper() and isdigit(), and you can call those in Django templates using the same dot syntax:

>>> from django.template import Template, Context 
>>> t = Template('{{ var }} -- {{ var.upper }} -- {{ var.isdigit }}') 
>>> t.render(Context({'var': 'hello'})) 
'hello -- HELLO -- False' 
>>> t.render(Context({'var': '123'})) 
'123 -- 123 -- True' 

Note that you do not include parentheses in the method calls. Also, it's not possible to pass arguments to the methods; you can only call methods that have no required arguments. (We explain this philosophy later in this chapter.) Finally, dots are also used to access list indices, for example:

>>> from django.template import Template, Context 
>>> t = Template('Item 2 is {{ items.2 }}.') 
>>> c = Context({'items': ['apples', 'bananas', 'carrots']}) 
>>> t.render(c) 
'Item 2 is carrots.' 

Negative list indices are not allowed. For example, the template variable

{{ items.-1 }} would cause a TemplateSyntaxError.

Dot lookups can be summarized like this: when the template system encounters a dot in a variable name, it tries the following lookups, in this order:

The system uses the first lookup type that works. It's short-circuit logic. Dot lookups can be nested multiple levels deep. For instance, the following example uses {{ person.name.upper }}, which translates into a dictionary lookup (person['name']) and then a method call (upper()):

>>> from django.template import Template, Context 
>>> person = {'name': 'Sally', 'age': '43'} 
>>> t = Template('{{ person.name.upper }} is {{ person.age }} years old.') 
>>> c = Context({'person': person}) 
>>> t.render(c) 
'SALLY is 43 years old.' 

Method calls are slightly more complex than the other lookup types. Here are some things to keep in mind:

        >>> t = Template("My name is {{ person.first_name }}.") 
        >>> class PersonClass3: 
        ...     def first_name(self): 
        ...         raise AssertionError("foo") 
        >>> p = PersonClass3() 
        >>> t.render(Context({"person": p})) 
        Traceback (most recent call last): 
        ... 
        AssertionError: foo 
         
        >>> class SilentAssertionError(Exception): 
        ...     silent_variable_failure = True 
        >>> class PersonClass4: 
        ...     def first_name(self): 
        ...         raise SilentAssertionError 
        >>> p = PersonClass4() 
        >>> t.render(Context({"person": p})) 
        'My name is .' 

        def delete(self): 
        # Delete the account 
        delete.alters_data = True 

Generally, if a variable doesn't exist, the template system inserts the value of the engine's string_if_invalid configuration option, which is an empty string by default. For example:

>>> from django.template import Template, Context 
>>> t = Template('Your name is {{ name }}.') 
>>> t.render(Context()) 
'Your name is .' 
>>> t.render(Context({'var': 'hello'})) 
'Your name is .' 
>>> t.render(Context({'NAME': 'hello'})) 
'Your name is .' 
>>> t.render(Context({'Name': 'hello'})) 
'Your name is .' 

This behavior is better than raising an exception because it's intended to be resilient to human error. In this case, all of the lookups failed because variable names have the wrong case or name. In the real world, it's unacceptable for a web site to become inaccessible due to a small template syntax error.