小学生学python（七）练习

我天天练习，天天都在熟悉

1. 生成一个文件，文件名为pack.dat，大小为1G

import  time
def createbigfile(n):
    local_time = time.strftime('%Y%m%d_%H%M%S', time.localtime())
    #file_path = 'bigfile'+ str(local_time) + '.log'
    file_path = 'pack.dat'
    f = open(file_path, 'w')
    f.seek(1024*1024*1024*int(n))
    f.write('testfile')
    f.close()


if __name__ == '__main__':
    n = input('请输入需要生成几个G大小的文件:')
    createbigfile(n)

 2.读取一个xml文件

假设一个country_data.xml

<?xml version="1.0"?>

<data>


<country name="Liechtenstein">

<rank>1</rank>

<year>2008</year>

<gdppc>141100</gdppc>

<neighbor name="Austria" direction="E"/>

<neighbor name="Switzerland" direction="W"/>

</country>


<country name="Singapore">

<rank>4</rank>

<year>2011</year>

<gdppc>59900</gdppc>

<neighbor name="Malaysia" direction="N"/>

</country>


<country name="Panama">

<rank>68</rank>

<year>2011</year>

<gdppc>13600</gdppc>

<neighbor name="Costa Rica" direction="W"/>

<neighbor name="Colombia" direction="E"/>

</country>

</data>

对其进行操作

from xml.etree import ElementTree as ET
tree = ET.parse('country_data.xml')
root = tree.getroot()
print(root.tag)
for child in root:
    print(child.tag, child.attrib)
# 取指定数据
print(root[0][0].text)  #rank的值
print(root[0][1].text)  #year的值

# 取感兴趣的数据
for neighbor in root.iter('neighbor'):
    print(neighbor.attrib)

for country in root.findall('country'):
    rank = country.find('rank').text
    name = country.get('name')
    print(name, rank)

# 修改文件
for rank in root.iter('rank'):
    new_rank = int(rank.text) + 1
    rank.text = str(new_rank)
    rank.set('updated', 'y')
tree.write('output.xml')

for country in root.findall('country'):
    rank = int(country.find('rank').text)
    if rank > 60:
        root.remove(country)
tree.write('output.xml')

 但是，这个方式在遇到编码方式是GB的时候，就会报错误

ValueError: multi-byte encodings are not supported

比如

<?xml version="1.0" encoding="GB2312"?>

<date>

</date>

可以使用库lxml，比如

from lxml import etree
xml = etree.parse("http_cpack.xml")
print(etree.tostring(xml))
print(xml.xpath('//*'))
print(xml.xpath('//conds'))
print(xml.xpath('//conds//cond[@value="32220401"]'))