python用str方法替换字符串中的多个元素 [英] python replace multiple elements in string with str methods

问题描述

你好，我正在学习用python编程。我想写一个函数，需要一串DNA并返回赞美，我一直试图解决这一段时间，并通过python文档看，但无法工作出来。我已经写了函数的文档字符串，所以你可以看到答案应该是什么样子。我在这个论坛上看到过类似的问题，但我无法理解答案。如果有人能用str格式和循环/ if语句解释这个问题，我将不胜感激，因为我还没有详细研究字典/列表。提前感谢您

我尝试了str.replace，但无法让它为多个元素工作，试图嵌套if语句，这也没有工作。然后我试着写4个单独的循环，但无济于事。

  def get_complementary_sequence（dna）：
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ; get_complementary_sequence（'AT'）
 TA 
>>> get_complementary_sequence（'GCTTAA'）
 CGAATT 
 

 
 for char in dna：
 if char == A：
 dna = dna.replace（'A'，'T'）
 elif char == T：
 dna = dna.replace（'T'，'A'）
＃...等等
  

您可能不需要创建具有所有可能组合的翻译表格。 / p>

 >>> M = {'A'：'T'，'T'：'A'，'C'：'G'，'G'：'C'} 
>>> STR ='CGAATT'
>>> S =.join（[M.get（c，c）for c in STR]）
>>> S 
'GCTTAA'
  

这是如何工作的：

 ＃这将根据你的字典返回一个char列表M 
>>> L = [M.get（c，c）对于c中的STR] 
>>> L 
 ['G'，'C'，'T'，'T'，'A'，'A'] 
  

join（）方法返回一个字符串，其中序列的字符串元素已经被str分隔符连接。

 >>> str = - 
>>> L = ['a'，'b'，'c'] 
>>> str.join（L）
'a-b-c'
  

Hello I am learning to program with python. I am trying to write a function that takes a string of DNA and returns the compliment, I have been trying to solve this for a while now and looked through the python documentation but couldn't work it out. I have written the doc string for the function so you can see what the answer should look like. I have seen a similar question asked on this forum but I could not understand the answers. I would be grateful if someone can explain this using only str formatting and loops / if statements, as I have not yet studied dictionaries/lists in detail. thank you in advance

I tried str.replace but could not get it to work for multiple elements, tried nested if statements and this didn't work either. I then tried writing 4 separate for loops, but to no avail.

def get_complementary_sequence(dna):

    """ (str) -> str

    Return the DNA sequence that is complementary 
    to the given DNA sequence.

    >>> get_complementary_sequence('AT')
    TA
    >>> get_complementary_sequence('GCTTAA')
    CGAATT

    """

    for char in dna:
        if char == A:
            dna = dna.replace('A', 'T')
        elif  char == T:
            dna = dna.replace('T', 'A')
        # ...and so on

解决方案

You can map each letter to another letter.

You probably need not create translation table with all possible combination.

>>> M = {'A':'T', 'T':'A', 'C':'G', 'G':'C'}
>>> STR = 'CGAATT'
>>> S = "".join([M.get(c,c) for c in STR])
>>> S
'GCTTAA'

How this works:

# this returns a list of char according to your dict M
>>> L = [M.get(c,c) for c in STR]  
>>> L
['G', 'C', 'T', 'T', 'A', 'A']

The method join() returns a string in which the string elements of sequence have been joined by str separator.

>>> str = "-"
>>> L = ['a','b','c']
>>> str.join(L)
'a-b-c'

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