在Python中实现替换字符串中的子串的示例

假如有个任务： 给定一个字符串，通过查询字典，来替换给定字符中的变量。如果使用通常的方法：

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

其实可以使用string.Template类来实现上面的替换

>>> from string import Template
>>> words = Template("This is $var")
>>> print(words.substitute({"var": "dog"})) # 通过字典的方式来传参
This is dog
>>> print(words.substitute(var="dog"))   # 通过关键字方式来传参
This is dog
>>>

在创建Template实例时，在字符串格式中，可以使用两个美元符来代替$，还可以用${}将 变量扩起来，这样的话，变量后面还可以接其他字符或数字，这个使用方式很像Shell或者Perl里面的语言。下面以letter模板来示例一下:

>>> 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
>>>

有时候，为了给substitute准备一个字典做参数，最简单的方法是设定一些本地变量，然后将这些变量交给local()(此函数创建一个字典，字典中的key就是本地变量，本地变量的值通过key来访问)。

>>> locals()   # 刚进入时，没有其他变量
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', '__doc__': None, '__package__': None}
>>> name = "Alice" # 创建本地变量name 
>>> age = 18   # 创建本地变量age
>>> locals()   # 再执行locals()函数就可以看到name, age的键值队
{'name': 'Alice', '__builtins__': <module '__builtin__' (built-in)>, 'age': 18, '__package__': None, '__name__': '__mai
__', '__doc__': None}
>>> locals()["name"] # 通过键name来获取值
'Alice'
>>> locals()["age"] # 通过键age来获取值
18
>>>

有了上面的例子打底来看一个示例：

>>> 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

另外一种方法是使用关键字参数语法而非字典，直接将值传递给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
>>>

甚至可以同时传递字典和关键字

>>> 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
>>>

为了防止字典的条目和关键字参数显示传递的值发生冲突，关键字参数优先，比如:

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

以上这篇在Python中实现替换字符串中的子串的示例就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持三水点靠木。