dynamic setattr

[Mariano Di Felice]

Hi,
I have a property file (.ini) that has multiple sections and relative keys, as default structure.

Now, I would like to export from my utility class methods getter and setter.
I have started as is:

class Utility:

keys = {"STANDUP": ["st_key1", "st_key2", "st_key3", "st_key4"],
"DEFAULT": ["def_key1", "def_key2", "def_key3", "def_key4", "def_key5"]}


def __init__(self):
for section, keyList in keys .items():
for key in keyList:
setattr(self, "get_%s" % key, self.get_value(section, key))
setattr(self, "set_%s" % key, lambda value:self.set_value(section, key, value) )

def get_value(section, key):
if file_ini.has_option(section, key):
return lambda: file_ini.get(section, key)
return lambda: None

def set_value(section, key, value):
print "set section: %s - key: %s - value: %s" % (section, key, value)
if file_ini.has_option(section, key):
file_ini.set(section , key ,value)


if __name__ == "__main__":
utility = Utility()
print "key2: %s" % utility.get_def_key2() ## -> value return 100
print "set value 50 to def_key2"
utility.set_def_key2(50)
print "new value def_key2: %s" % utility.get_def_key2() ## -> value return 100


Well, when in code I set value 50 to def_key2, return value of key st_key4 of STANDUP section!!!! Why?
"set section STANDUP - key st_key4 - value: 200"

Can anyone help me, please???

Thx in Advance

 

[Steven D'Aprano]

Hi,
I have a property file (.ini) that has multiple sections and relative
keys, as default structure.

Have you looked at Python's standard INI file library?

http://docs.python.org/library/configparser.html

Now, I would like to export from my utility class methods getter and
setter. I have started as is:

class Utility:

keys = {"STANDUP": ["st_key1", "st_key2", "st_key3", "st_key4"],
"DEFAULT": ["def_key1", "def_key2", "def_key3",
"def_key4", "def_key5"]}

This defines a *shared* class attribute. As it is attached to the class,
not an instance, every instance will see the same shared dict.

def __init__(self):
for section, keyList in keys .items():
for key in keyList:

As given, this is a SyntaxError. Please do not retype your code from
memory, always COPY AND PASTE your actual code.

In this case, it is easy to fix the syntax error by fixing the
indentation. But what other changes have you made by accident?

Your code:

def __init__(self):
for section, keyList in keys .items():

looks for a *global variable* called keys, *not* the shared class
attribute Utility.keys. By design, attributes are not in the function
scope. If you want to access an attribute, whether class or instance, you
must always refer to them as attributes.


def __init__(self):
for section, keyList in self.keys.items(): # this will work

setattr(self, "get_%s" % key, self.get_value(section,
key))
setattr(self, "set_%s" % key, lambda
value:self.set_value(section, key, value) )

What a mess. What is the purpose of this jumble of code?

My guess is that you are experienced with Java, and you are trying to
adapt Java idioms and patterns to Python. Before you do this, you should
read these two articles by a top Python developer who also knows Java
backwards:

http://dirtsimple.org/2004/12/python-is-not-java.html
http://dirtsimple.org/2004/12/java-is-not-python-either.html

if __name__ == "__main__":
utility = Utility()
print "key2: %s" % utility.get_def_key2() ## -> value return 100

Again, another SyntaxError. This can be fixed. But the next part cannot.

Except for two comments, 100 does not exist in your sample code. Python
doesn't magically set values to 100. The code you give cannot possibly
return 100 since nowhere in your code does it set anything to 100.

If you actually run the code you provide (after fixing the SyntaxErrors),
you get this error:

py> utility = Utility()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 5, in __init__
NameError: global name 'keys' is not defined


If you fix that and try again, you get this error:

py> utility = Utility()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 7, in __init__
TypeError: get_value() takes exactly 2 arguments (3 given)


The results you claim you get are not true.


Please read this page and then try again:

http://sscce.org/

 

[Mariano Di Felice]

Hi Steven,
Sorry for inconvenients.
I've posted "unsyntax" example just typing from here, just for exaplain my problem

Finally, I don't understand why every set_<key> set value on wrong section/key.
I think setattr syntax is correct, but it doesn't works!

About java/python concept, yeah! You all right!
But I need a conversion class (as Utility) that expose getter/setter of anykeys.

Thx!

Il giorno venerdì 27 luglio 2012 15:46:59 UTC+2, Steven D'Aprano ha scritto:

On Fri, 27 Jul 2012 05:49:45 -0700, Mariano Di Felice wrote:

&gt; Hi,
&gt; I have a property file (.ini) that has multiple sections and relative
&gt; keys, as default structure.

Have you looked at Python's standard INI file library?

I already use it!

http://docs.python.org/library/configparser.html


&gt; Now, I would like to export from my utility class methods getter and
&gt; setter. I have started as is:
&gt;
&gt; class Utility:
&gt;
&gt; keys = {&quot;STANDUP&quot;: [&quot;st_key1&quot;, &quot;st_key2&quot;, &quot;st_key3&quot;, &quot;st_key4&quot;],
&gt; &quot;DEFAULT&quot;: [&quot;def_key1&quot;, &quot;def_key2&quot;, &quot;def_key3&quot;,
&gt; &quot;def_key4&quot;, &quot;def_key5&quot;]}

This defines a *shared* class attribute. As it is attached to the class,
not an instance, every instance will see the same shared dict.


&gt; def __init__(self):
&gt; for section, keyList in keys .items():
&gt; for key in keyList:

As given, this is a SyntaxError. Please do not retype your code from
memory, always COPY AND PASTE your actual code.

In this case, it is easy to fix the syntax error by fixing the
indentation. But what other changes have you made by accident?

Your code:

def __init__(self):
for section, keyList in keys .items():

looks for a *global variable* called keys, *not* the shared class
attribute Utility.keys. By design, attributes are not in the function
scope. If you want to access an attribute, whether class or instance, you
must always refer to them as attributes.


def __init__(self):
for section, keyList in self.keys.items(): # this will work


&gt; setattr(self, &quot;get_%s&quot; % key, self.get_value(section,
&gt; key))
&gt; setattr(self, &quot;set_%s&quot; % key, lambda
&gt; value:self.set_value(section, key, value) )


What a mess. What is the purpose of this jumble of code?

My guess is that you are experienced with Java, and you are trying to
adapt Java idioms and patterns to Python. Before you do this, you should
read these two articles by a top Python developer who also knows Java
backwards:

http://dirtsimple.org/2004/12/python-is-not-java.html
http://dirtsimple.org/2004/12/java-is-not-python-either.html



&gt; if __name__ == &quot;__main__&quot;:
&gt; utility = Utility()
&gt; print &quot;key2: %s&quot; % utility.get_def_key2() ## -&gt; value return 100

Again, another SyntaxError. This can be fixed. But the next part cannot.

Except for two comments, 100 does not exist in your sample code. Python
doesn't magically set values to 100. The code you give cannot possibly
return 100 since nowhere in your code does it set anything to 100.

If you actually run the code you provide (after fixing the SyntaxErrors),
you get this error:

py&gt; utility = Utility()
Traceback (most recent call last):
File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
File &quot;&lt;stdin&gt;&quot;, line 5, in __init__
NameError: global name 'keys' is not defined


If you fix that and try again, you get this error:

py&gt; utility = Utility()
Traceback (most recent call last):
File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
File &quot;&lt;stdin&gt;&quot;, line 7, in __init__
TypeError: get_value() takes exactly 2 arguments (3 given)


The results you claim you get are not true.


Please read this page and then try again:

http://sscce.org/