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在Python中實(shí)現(xiàn)替換字符串中的子串的示例

更新時(shí)間：2018年10月31日 09:17:58 作者：杰瑞26

今天小編就為大家分享一篇在Python中實(shí)現(xiàn)替換字符串中的子串的示例，具有很好的參考價(jià)值，希望對大家有所幫助。一起跟隨小編過來看看吧

假如有個(gè)任務(wù)：給定一個(gè)字符串，通過查詢字典，來替換給定字符中的變量。如果使用通常的方法：

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

其實(shí)可以使用string.Template類來實(shí)現(xiàn)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(guān)鍵字方式來傳參
This is dog
>>>

在創(chuàng)建Template實(shí)例時(shí)，在字符串格式中，可以使用兩個(gè)美元符來代替$，還可以用${}將變量擴(kuò)起來，這樣的話，變量后面還可以接其他字符或數(shù)字，這個(gè)使用方式很像Shell或者Perl里面的語言。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(shí)候，為了給substitute準(zhǔn)備一個(gè)字典做參數(shù)，最簡單的方法是設(shè)定一些本地變量，然后將這些變量交給local()(此函數(shù)創(chuàng)建一個(gè)字典，字典中的key就是本地變量，本地變量的值通過key來訪問)。

>>> locals()   # 剛進(jìn)入時(shí)，沒有其他變量
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', '__doc__': None, '__package__': None}
>>> name = "Alice" # 創(chuàng)建本地變量name 
>>> age = 18   # 創(chuàng)建本地變量age
>>> locals()   # 再執(zhí)行l(wèi)ocals()函數(shù)就可以看到name, age的鍵值隊(duì)
{'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(gè)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(guān)鍵字參數(shù)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(shí)傳遞字典和關(guān)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(guān)鍵字參數(shù)顯示傳遞的值發(fā)生沖突，關(guān)鍵字參數(shù)優(yōu)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

以上這篇在Python中實(shí)現(xiàn)替換字符串中的子串的示例就是小編分享給大家的全部內(nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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