Codewars第二天–Complementary DNA

开始在Codewars刷Python3题，发现基本知识都忘完了，边刷边复习边记录。

8kyu>>7kyu

Deoxyribonucleic acid (DNA) is a chemical found in the nucleus of cells and carries the "instructions" for the development and functioning of living organisms.If you want to know more http://en.wikipedia.org/wiki/DNAIn DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". You have function with one side of the DNA (string, except for Haskell); you need to get the other complementary side. DNA strand is never empty or there is no DNA at all (again, except for Haskell).DNA_strand ("ATTGC") # return "TAACG"DNA_strand ("GTAT") # return "CATA"

这个题目其实很简单，就是执行一个DNA转RNA的过程，给定一个DNA单链字符串，输出与之对应的RNA字符串。

开始自己想得很复杂了，想着弄成列表，结果输出还要转换成字符串。。。

在这里只需要写一个类似switch的判断就好了，然后再用join()把每一个转换好的RNA字符链接成字符串输出就好了。

代码如下：

def DNA_strand(dna):    # code here    my = {            "A" : "T",            "T" : "A",            "C" : "G",            "G" : "C",            }    return "".join(my[i] for i in dna)

代码中my 实现了对输入的DNA字符串进行转换的过程。

join()用法：

用于将序列中的元素以指定的字符链接生成一个新的字符串。也就是使用它之后生成的只能是字符串。