python，通过坐标从DAS获取序列

Question

ucsc DAS server，通过坐标得到DNA序列。在

网址：http://genome.ucsc.edu/cgi-bin/das/hg19/dna?segment=chr20:30037432,30038060

示例文件：

<DASDNA>
  <SEQUENCE id="chr20" start="30037832" stop="30038060" version="1.00">
  <DNA length="229">
    gtggcacccaaagatgctggaatctttatggcaaatgccgttacagatgc            
    tccaagaaggaaagagtctatgtttactgcataaataataaaatgtgctg     
    cgtgaagcccaagtaccagccaaaagaaaggtggtggccattttaactgc 
    tttgaagcctgaagccatgaaaatgcagatgaagctcccagtggattccc 
    acactctatcaataaacacctctggctga
  </DNA>
  </SEQUENCE>
</DASDNA>

我想要的是这个部分：

^{pr2}$

我想从数千个这样的网址序列部分，我应该怎么做？ 我试图将数据写入文件并解析该文件，它工作正常，但是有没有任何方法可以直接解析类似xml的字符串？我试过其他帖子中的一些例子，但都没用。在

在这里，我添加了我的解决方案。感谢下面的两个答案。

解决方案1:

def getSequence2(chromosome, start, end):
    base = 'http://genome.ucsc.edu/cgi-bin/das/hg19/dna?segment='
    url = base + chromosome + ':' + str(start) + ',' + str(end)
    doc = etree.parse(url,parser=etree.XMLParser())
    if doc != '':
        sequence = doc.xpath('SEQUENCE/DNA/text()')[0].replace('\n','')
    else:
        sequence = 'THE SEQUENCE DOES NOT EXIST FOR GIVEN COORDINATES'
    return sequence

解决方案2:

def getSequence1(chromosome, start, end):
    base = 'http://genome.ucsc.edu/cgi-bin/das/hg19/dna?segment='
    url = base + chromosome + ':' + str(start) + ',' + str(end)
    xml = urllib2.urlopen(url).read()
    if xml != '':
        w = open('temp.xml', 'w')
        w.write(xml)
        w.close()
        dom = parse('temp.xml')
        data = dom.getElementsByTagName('DNA')
        sequence = data[0].firstChild.nodeValue.replace('\n','')
    else: 
        sequence = 'THE SEQUENCE DOES NOT EXIST FOR GIVEN COORDINATES'
    return sequence

当然，他们需要导入一些必要的库。在

Answer 1

使用像lxml这样的pythonxml解析库，用该解析器加载XML文件，然后使用选择器（例如使用XPath）获取所需的节点/元素。在

Answer 2

>>> from lxml import etree
>>> doc = etree.parse("http://genome.ucsc.edu/cgi-bin/das/hg19/dna?segment=chr20:30037432,30038060",parser=etree.XMLParser())
>>> doc.xpath('SEQUENCE/DNA/text()')
['\natagtggcacatgtctgttgtcctagctcctcggggaaactcaggtggga\ngagtcccttgaactgggaggaggaggtttgcagtgagccagaatcattcc\nactgtactccagcctaggtgacagagcaagactcatctcaaaaaaaaaaa\naaaaaaaaaaaaaagacaatccgcacacataaaggctttattcagctgat\ngtaccaaggtcactctctcagtcaaaggtgggaagcaaaaaaacagagta\naaggaaaaacagtgatagatgaaaagagtcaaaggcaagggaaacaaggg\naccttctatctcatctgtttccattcttttacagacctttcaaatccgga\ngcctacttgttaggactgatactgtctcccttctttctgctttgtgtcag\ngtggcacccaaagatgctggaatctttatggcaaatgccgttacagatgc\ntccaagaaggaaagagtctatgtttactgcataaataataaaatgtgctg\ncgtgaagcccaagtaccagccaaaagaaaggtggtggccattttaactgc\ntttgaagcctgaagccatgaaaatgcagatgaagctcccagtggattccc\nacactctatcaataaacacctctggctga\n']