假如有個任務: 給定一個字串，通過查詢字典，來替換給定字元中的變數。如果使用通常的方法:

>>> "This is a %(var)s" % {"var":"dog"}
'This is a dog'
>>>

其實可以使用string.Template類來實現上面的替換

>>> from string import Template
>>> words = Template("This is $var")
>>> print(words.substitute({"var": "dog"}))    # 通過字典的方式來傳參
This is dog
>>> print(words.substitute(var="dog"))         # 通過關鍵字方式來傳參
This is dog
>>>
 

在建立Template例項時，在字串格式中，可以使用兩個美元符來代替$，還可以用${}將 變數擴起來，這樣的話，變數後面還可以接其他字元或數字，這個使用方式很像Shell或者Perl裡面的語言。下面以letter模板來示例一下:

>>> from string import Template
>>> letter = """Dear $customer,
... I hope you are having a great time!
... If you do not find Room $room to your satisfaction, let us know.
... Please accept this $$5 coupon.
...                 Sincerely,
...                 $manager,
...                 ${name}Inn"""
>>> template = Template(letter)
>>> letter_dict = {"name": "Sleepy", "customer": "Fred Smith", "manager": "Tom Smith", "room": 308}
>>> print(template.substitute(letter_dict))
Dear Fred Smith,
I hope you are having a great time!
If you do not find Room 308 to your satisfaction, let us know.
Please accept this $5 coupon.
                Sincerely,
                Tom Smith,
                SleepyInn
>>>
 

有時候，為了給substitute準備一個字典做引數，最簡單的方法是設定一些本地變數，然後將這些變數交給local()(此函式建立一個字典，字典中的key就是本地變數，本地變數的值通過key來訪問)。

>>> locals()         # 剛進入時，沒有其他變數
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', '__doc__': None, '__package__': None}
>>> name = "Alice"   # 建立本地變數name 
>>> age = 18         # 建立本地變數age
>>> locals()         # 再執行locals()函式就可以看到name, age的鍵值隊
{'name': 'Alice', '__builtins__': <module '__builtin__' (built-in)>, 'age': 18, '__package__': None, '__name__': '__mai
__', '__doc__': None}
>>> locals()["name"] # 通過鍵name來獲取值
'Alice'
>>> locals()["age"]  # 通過鍵age來獲取值
18
>>>

 

有了上面的例子打底來看一個示例:

>>> from string import Template
>>> msg = Template("The square of $number is $square")
>>> for number in range(10):
...     square = number * number
...     print msg.substitute(locals())
...
The square of 0 is 0
The square of 1 is 1
The square of 2 is 4
The square of 3 is 9

另外一種方法是使用關鍵字引數語法而非字典，直接將值傳遞給substitute。

>>> from string import Template
>>> msg = Template("The square of $number is $square")
>>> for i in range(4):
...     print msg.substitute(number=i, square=i*i)
...
The square of 0 is 0
The square of 1 is 1
The square of 2 is 4
The square of 3 is 9
>>>

 甚至可以同時傳遞字典和關鍵字

>>> from string import Template
>>> msg = Template("The square of $number is $square")
>>> for number in range(4):
...     print msg.substitute(locals(), square=number*number)
...
The square of 0 is 0
The square of 1 is 1
The square of 2 is 4
The square of 3 is 9
>>>

為了防止字典的條目和關鍵字引數顯示傳遞的值發生衝突，關鍵字引數優先，比如:

>>> from string import Template
>>> msg = Template("It is $adj $msg")
>>> adj = "interesting"
>>> print(msg.substitute(locals(), msg="message"))
It is interesting message