内置类型错误：必须为str，而不是bytes

Question

我把我的脚本从Python 2.7转换到了3.2版本，但现在遇到了一个错误。

# -*- coding: utf-8 -*-
import time
from datetime import date
from lxml import etree
from collections import OrderedDict

# Create the root element
page = etree.Element('results')

# Make a new document tree
doc = etree.ElementTree(page)

# Add the subelements
pageElement = etree.SubElement(page, 'Country',Tim = 'Now', 
                                      name='Germany', AnotherParameter = 'Bye',
                                      Code='DE',
                                      Storage='Basic')
pageElement = etree.SubElement(page, 'City', 
                                      name='Germany',
                                      Code='PZ',
                                      Storage='Basic',AnotherParameter = 'Hello')
# For multiple multiple attributes, use as shown above

# Save to XML file
outFile = open('output.xml', 'w')
doc.write(outFile) 

在最后一行，我收到了这个错误：

builtins.TypeError: must be str, not bytes
File "C:\PythonExamples\XmlReportGeneratorExample.py", line 29, in <module>
  doc.write(outFile)
File "c:\Python32\Lib\site-packages\lxml\etree.pyd", line 1853, in lxml.etree._ElementTree.write (src/lxml/lxml.etree.c:44355)
File "c:\Python32\Lib\site-packages\lxml\etree.pyd", line 478, in lxml.etree._tofilelike (src/lxml/lxml.etree.c:90649)
File "c:\Python32\Lib\site-packages\lxml\etree.pyd", line 282, in lxml.etree._ExceptionContext._raise_if_stored (src/lxml/lxml.etree.c:7972)
File "c:\Python32\Lib\site-packages\lxml\etree.pyd", line 378, in lxml.etree._FilelikeWriter.write (src/lxml/lxml.etree.c:89527)

我已经安装了Python 3.2，也安装了lxml-2.3.win32-py3.2.exe。

在Python 2.7上，这个脚本是可以正常运行的。

Answer 1

如果因为某种原因，输出文件是用 mode='w' 打开的，而不能用 'wb' 重新打开，那么可以采用一个变通的方法。你可以通过访问 TextIOWrapper 的 .buffer 属性来创建一个 BufferedWriter（这个对象在用 mode='wb' 打开文件时会自动生成），然后就可以进行写入操作了。

s = """
<country name="Liechtenstein">
    <year>2008</year>
    <gdppc>141100</gdppc>
</country>
"""
import xml.etree.ElementTree as ET
doc = ET.ElementTree(ET.fromstring(s))

outFile = open('output.xml', 'w')
doc.write(outFile.buffer)             # <--- buffer here
outFile.close()

Answer 2

将二进制文件转换为Base64格式，以及反向操作。用Python 3.5.2来证明这一点。

import base64

read_file = open('/tmp/newgalax.png', 'rb')
data = read_file.read()

b64 = base64.b64encode(data)

print (b64)

# Save file
decode_b64 = base64.b64decode(b64)
out_file = open('/tmp/out_newgalax.png', 'wb')
out_file.write(decode_b64)

# Test in python 3.5.2

Answer 3

输出文件应该以二进制模式打开。

outFile = open('output.xml', 'wb')