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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN-US style='font-size:9.0pt;font-family:Arial'>Hi,<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN-US style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN-US style='font-size:9.0pt;font-family:Arial'>I
am learning metaclass by reading “Metaclass programming in Python, Part <st1:chmetcnv
TCSC="0" NumberType="1" Negative="False" HasSpace="False" SourceValue="2"
UnitName="”" w:st="on">2”</st1:chmetcnv>. I have a question as
following and had tried to search from internet and also have read the article
“Unifying types and classes in Python <st1:chmetcnv TCSC="0"
NumberType="1" Negative="False" HasSpace="False" SourceValue="2.2" UnitName="”"
w:st="on">2.2”</st1:chmetcnv> but failed to get satisfied answer. Could
you please give me any comments to enlighten me? Thank you very much.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN-US style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>{{{<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
inheritance inheritance<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
object -------------> type -------------> Printable(Printable.__str__)<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
|
.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
|
. instantiation<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
|
.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
|
v<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
----------------------------------------> C(?)<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
. instantiation<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
v<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#
c(?)<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>#<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>>>>
class Printable(type):<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>...
def __str__(cls):<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>...
return "This is class %s" % cls.__name__<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>...<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>>>>
class C(object):<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>...
__metaclass__ = Printable<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>...<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=red face=Arial><span lang=EN style='font-size:9.0pt;font-family:
Arial;color:red'>>>> print C
#
equivalent to print Printable.__str__(C)<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>This
is class C<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>>>>
c = C()<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>>>>
print
c
# equivalent to print C.__str__(c)<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'><__main__.C
object at 0x1870dacc><o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=red face=Arial><span lang=EN style='font-size:9.0pt;font-family:
Arial;color:red'>>>> C.__str__<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=red face=Arial><span lang=EN style='font-size:9.0pt;font-family:
Arial;color:red'><slot wrapper '__str__' of 'object' objects><o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>>>>
print C<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>This
is class C<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>}}}<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>The
question is why Printable.__str__ is invoked while executing “print
C” but “C.__str__” shows it is resolved as
“objct.__str__”? <o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 face=Arial><span lang=EN style='font-size:9.0pt;font-family:Arial'>Wish
I can get reply from you. Really thanks.<o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=black face=Arial><span lang=EN-US style='font-size:9.0pt;
font-family:Arial;color:black'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=black face=Arial><span lang=EN-US style='font-size:8.0pt;
font-family:Arial;color:black'>Best Regards,</span></font><font color=black><span
lang=EN-US style='color:black'><o:p></o:p></span></font></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><font
size=1 color=black face=Arial><span lang=EN-US style='font-size:8.0pt;
font-family:Arial;color:black'><br>
<st1:PersonName ProductID="Tommy Zong" w:st="on">Tommy Zong</st1:PersonName><br>
Chengdu Jiehua Technologies Co, Ltd.<br>
Tel: 86-28-85148500-654<br>
Mail: </span></font><font color=black><span lang=EN-US style='color:black'><a
href="mailto:tzong@sigma-rt.com" title="mailto:tzong@sigma-rt.com"><font
size=1 face=Arial><span style='font-size:8.0pt;font-family:Arial'>tzong@sigma-rt.com</span></font></a></span></font><font
size=1 color=purple face=Arial><span lang=EN-US style='font-size:8.0pt;
font-family:Arial;color:purple'><br>
</span></font><font size=1 color=black face=Arial><span lang=EN-US
style='font-size:8.0pt;font-family:Arial;color:black'>MSN: </span></font><font
color=black><span lang=EN-US style='color:black'><a
href="mailto:metalzong@163.com" title="mailto:metalzong@163.com"><font size=1
face=Arial><span style='font-size:8.0pt;font-family:Arial'>metalzong@163.com</span></font></a><o:p></o:p></span></font></p>
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