Re: Need help understanding list structure
On 2016-05-03 18:54, Dan Strohl via Python-list wrote: I added a __repr__ method at the end of the gedcom library like so: def __repr__(self): """ Format this element as its original string """ result = repr(self.level()) if self.pointer() != "": result += ' ' + self.pointer() result += ' ' + self.tag() if self.value() != "": result += ' ' + self.value() return result and now I can print myList properly. Eric and Michael also mentioned repr above, but I guess I needed someone to spell it out for me. Thanks for taking the time to put it in terms an old dog could understand. Glad to help! (being an old dog myself, I know the feeling!) One other point for you, if your "__repr__(self)" code is the same as the "__str__(self)" code (which it looks like it is, at a glance at least), you can instead reference the __str__ method and save having a duplicate code block... some examples: = Option 1: This is the easiest to read (IMHO) and allows for the possibility that str() is doing something here like formatting or whatever. (in this case it shouldn't be though). However, to call this actually is taking multiple steps (calling object.__repr__, whch calls str(), which calls object.__str__(). ) def __repr__(self): return str(self) = Option 2: this isn't hard to read, and just takes two steps (calling object.__repr__(), which calls object.__str__(). def __repr__(self): return self.__str__() Option 3: it's not that this is hard to read, but since it doesn't follow the standard "def blah(self):" pattern, sometimes I overlook these in the code (even when I put them there). This however is the shortest since it really just tells the object to return object.__str__() if either object.__repr__() OR object.__str__() is called. __repr__ = __str__ This probably doesn't matter much in this case, since it probably isn't called that much in normal use (though there are always exceptions), and in the end, Python is fast enough that unless you really need to slice off a few milliseconds, you will never notice the difference, but just some food for thought. Option 4: Delete the __str__ method. If there's no __str__, Python falls back to __repr__. If there's no __repr__, Python falls back to the somewhere> format. -- https://mail.python.org/mailman/listinfo/python-list
RE: Need help understanding list structure
> I added a __repr__ method at the end of the gedcom library like so: > > def __repr__(self): > """ Format this element as its original string """ > result = repr(self.level()) > if self.pointer() != "": > result += ' ' + self.pointer() > result += ' ' + self.tag() > if self.value() != "": > result += ' ' + self.value() > return result > > and now I can print myList properly. > > Eric and Michael also mentioned repr above, but I guess I needed someone > to spell it out for me. Thanks for taking the time to put it in terms an old > dog > could understand. > Glad to help! (being an old dog myself, I know the feeling!) One other point for you, if your "__repr__(self)" code is the same as the "__str__(self)" code (which it looks like it is, at a glance at least), you can instead reference the __str__ method and save having a duplicate code block... some examples: = Option 1: This is the easiest to read (IMHO) and allows for the possibility that str() is doing something here like formatting or whatever. (in this case it shouldn't be though). However, to call this actually is taking multiple steps (calling object.__repr__, whch calls str(), which calls object.__str__(). ) def __repr__(self): return str(self) = Option 2: this isn't hard to read, and just takes two steps (calling object.__repr__(), which calls object.__str__(). def __repr__(self): return self.__str__() Option 3: it's not that this is hard to read, but since it doesn't follow the standard "def blah(self):" pattern, sometimes I overlook these in the code (even when I put them there). This however is the shortest since it really just tells the object to return object.__str__() if either object.__repr__() OR object.__str__() is called. __repr__ = __str__ This probably doesn't matter much in this case, since it probably isn't called that much in normal use (though there are always exceptions), and in the end, Python is fast enough that unless you really need to slice off a few milliseconds, you will never notice the difference, but just some food for thought. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
I added a __repr__ method at the end of the gedcom library like so: def __repr__(self): """ Format this element as its original string """ result = repr(self.level()) if self.pointer() != "": result += ' ' + self.pointer() result += ' ' + self.tag() if self.value() != "": result += ' ' + self.value() return result and now I can print myList properly. Eric and Michael also mentioned repr above, but I guess I needed someone to spell it out for me. Thanks for taking the time to put it in terms an old dog could understand. -- https://mail.python.org/mailman/listinfo/python-list
RE: Need help understanding list structure
Take a look at the docs for print() https://docs.python.org/3.5/library/functions.html#print str() https://docs.python.org/3.5/library/stdtypes.html#str repr() https://docs.python.org/3.5/library/functions.html#repr When you do "print(object)", python will run everything through str() and output it. Str() will try to return a string representation of the object, what actually comes back will depend on how the objects author defined it. If object.__str__() has been defined, it will use that, if __str__() is not defined, it will use object.__repr__(). If object.__repr__() has not been defined, it will something that looks like "object_name object at xxx". So, as to your specific questions / comments: > At the risk of coming across as a complete dunder-head, I think my confusion > has to do with the type of data the library returns in the list. Any kind of > text > or integer list I manually create, doesn't do this. Actually, they do, but strings and integers have well defined __str__ and __repr__ methods, and behave pretty well. So... think about what is actually being passed to the print() function in each case: > print(type(myList)) Passing the string object of the results of type(myList) > print(len(myList)) Passing the integer object returning from len(myList) > print(myList[0]) Passing the gedcom ELEMENT object found at location 0 in the list > print(myList[0:29]) Passing a list object created by copying the items from location 0 to location 29 in the original list > print(myList) Passing the entire list object > for x in myList: > print(x) Passing the individual gedcom ELEMENT objects from the list. So, in each of these cases, you are passing different types of objects, and each one (string, integer, list, gedcom) will behave differently depending on how it is coded. > Why does printing a single item print the actual text of the object? If you are printing a single item (print(myList[0]), you are printing the __str__ or __repr__ for the object stored at that location. > Why does printing a range print the "representations" of the objects? If you are printing a range of objects, you are printing the __str__ or __repr__ for the RANGE OBJECT or LIST object, not the object itself, which apparently only checks for a __repr__() method in the contained gedcom ELEMENT objects, which is not defined (see below). > Why does iterating over the list print the actual text of the objects? When iterating over the list, you are printing the specific items again (just like when you did print(myList[0]) ) > How can I determine what type of data is in the list? Try print(type(myList[0])), which will give you the type of data in the first object in the list (though, keep in mind that the object type could be different in each item in the list). If we look at the gedcom library (assuming you are talking about this one: https://github.com/madprime/python-gedcom/blob/master/gedcom/__init__.py) at the end of the file you can see they defined __str__() in the ELEMENT object, but there is no definition for __repr__(), which matches what we surmised above. If you want to fix it by editing the gedcom library, you could simply add a line at the end like: __repr__() = __str__() Hope that helps. Dan Strohl -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
At the risk of coming across as a complete dunder-head, I think my confusion has to do with the type of data the library returns in the list. Any kind of text or integer list I manually create, doesn't do this. See my questions down below at the end. If I run the following statements on the list returned by the gedcom library: print(type(myList)) print(len(myList)) print(myList[0]) print(myList[0:29]) print(myList) for x in myList: print(x) I get this: 29 0 HEAD [, , , , , , , , , , , , , , , , , , , , , , , , , , , , ] [, , , , , , , , , , , , , , , , , , , , , , , , , , , , ] 0 HEAD 1 SOUR AncestQuest 2 NAME Ancestral Quest 2 VERS 14.00.9 2 CORP Incline Software, LC 3 ADDR PO Box 95543 4 CONT South Jordan, UT 84095 4 CONT USA 1 DATE 3 MAY 2016 2 TIME 10:44:10 1 FILE test_gedcom.ged 1 GEDC 2 VERS 5.5 2 FORM LINEAGE-LINKED 1 CHAR ANSEL 0 @I1@ INDI 1 NAME John /Allen/ 1 SEX M 1 BIRT 2 DATE 1750 2 PLAC VA 1 DEAT 2 DATE 1804 2 PLAC KY 1 _UID D6C103E6105D654B85D47DA1B36E474BC7D1 1 CHAN 2 DATE 3 MAY 2016 3 TIME 10:43:35 0 TRLR Questions: Why does printing a single item print the actual text of the object? Why does printing a range print the "representations" of the objects? Why does iterating over the list print the actual text of the objects? How can I determine what type of data is in the list? -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
On Tue, May 3, 2016 at 11:21 PM, wrote: > Thanks for the replies. I definitely need a better understanding of " object at ADDRESS>" when using Python objects. So far no luck with web > searches or my Python books. Could someone point (no pun intended) me to a > good resource? > > Not that it matters, but the reason I got off track is there are pointers > within my data that point to other pieces of the data and have nothing to do > with Python. What you're seeing there is the default object representation. It isn't actually quoting an address but an "identity number". The only meaning of that number is that it's unique [1]; so if you see the same number come up twice in the list, you can be confident that the list has two references to the same object. Beyond that, it basically tells you nothing. So you know what kind of object it is, but anything else you'll have to figure out for yourself. ChrisA [1] Among concurrently-existing objects; if an object disappears, its ID can be reused. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
Thanks for the replies. I definitely need a better understanding of "" when using Python objects. So far no luck with web searches or my Python books. Could someone point (no pun intended) me to a good resource? Not that it matters, but the reason I got off track is there are pointers within my data that point to other pieces of the data and have nothing to do with Python. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
moa47...@gmail.com writes: > Am I correct in assuming that parsing a large text file would be > quicker returning pointers instead of strings? What do you mean by “return a pointer”? Python doesn't have pointers. In the Python language, a container type (such as ‘set’, ‘list’, ‘dict’, etc.) contains the objects directly. There are no “pointers” there; by accessing the items of a container, you access the items directly. What do you mean by “would be quicker”? I am concerned you are seeking speed of the program at the expense of understandability and clarity of the code. Instead, you should be writing clear, maintainable code. *Only if* the clear, maintainable code you write then actually ends up being too slow, should you then worry about what parts are quick or slow by *measuring* the specific parts of code to discover what is actually occupying the time. -- \ “All television is educational television. The question is: | `\ what is it teaching?” —Nicholas Johnson | _o__) | Ben Finney -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
On 05/02/2016 04:33 PM, moa47...@gmail.com wrote: > Yes, that does help. You're right. The author of the library I'm > using didn't implement either a __str__ or __repr__ method. Am I > correct in assuming that parsing a large text file would be quicker > returning pointers instead of strings? I've never run into this > before. I'm not sure what you mean by "returning pointers." The list isn't returning pointers. It's a list of *objects*. To be specific, a list of gedcom.Element objects, though they could be anything, including numbers or strings. If you refer to the source code where the Element class is defined you can see what these objects contain. I suspect they contain a lot more information than simply text. Lists of objects is a common idiom in Python. As you've discovered, if you shallow copy a list, the new list will contain the exact same objects. In many cases, this does not matter. For example a list of numbers, which are immutable or unchangeable objects. It doesn't matter that the instances are shared, since the instances themselves will never change. If the objects are mutable, as they are in your case, a shallow copy may not always be what you want. As to your question. A list never shows "pointers" as you say. A list always contains objects, and if you simply "print" the list, it will try to show a representation of the list, using the objects' repr dunder methods. Some classes I have used have their repr methods print out what the constructor would look like, if you were to construct the object yourself. This is very useful. If I recall, this is what BeautifulSoup objects do, which is incredibly useful. In your case, as Erik said, the objects you are dealing with don't provide repr dunder methods, so Python just lets you know they are objects of a certain class, and what their ids are, which is helpful if you're trying to determine if two objects are the same object. These are not "pointers" in the sense you're talking. You'll get text if the object prints text for you. This is true of any object you might store in the list. I hope this helps a bit. Exploring from the interactive prompt as you are doing is very useful, once you understand what it's saying to you. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
> When Python's "print" statement/function is invoked, it will print the > textual representation of the object according to its class's __str__ or > __repr__ method. That is, the print function prints out whatever text > the class says it should. > > For classes which don't implement a __str__ or __repr__ method, then > the text "" is used - where CLASS is the class > name and ADDRESS is the "memory pointer". > > > If I iterate over the list, I do get the actual text of each element > > and am able to use it. > > > > Also, if I iterate over the list and place each element in a new list > > using append, then each element in the new list is the text I expect > > not memory pointers. > > Look at the __iter__ method of the class of the object you are iterating > over. I suspect that it returns string objects, not the objects that are > in the list itself. > > String objects have a __str__ or __repr__ method that represents them as > the text, so that is what 'print' will output. > > Hope that helps, E. Yes, that does help. You're right. The author of the library I'm using didn't implement either a __str__ or __repr__ method. Am I correct in assuming that parsing a large text file would be quicker returning pointers instead of strings? I've never run into this before. -- https://mail.python.org/mailman/listinfo/python-list
Re: Need help understanding list structure
On 02/05/16 22:30, moa47...@gmail.com wrote: Can someone help me understand why or under what circumstances a list shows pointers instead of the text data? When Python's "print" statement/function is invoked, it will print the textual representation of the object according to its class's __str__ or __repr__ method. That is, the print function prints out whatever text the class says it should. For classes which don't implement a __str__ or __repr__ method, then the text "" is used - where CLASS is the class name and ADDRESS is the "memory pointer". > If I iterate over the list, I do get the actual text of each element > and am able to use it. > > Also, if I iterate over the list and place each element in a new list > using append, then each element in the new list is the text I expect > not memory pointers. Look at the __iter__ method of the class of the object you are iterating over. I suspect that it returns string objects, not the objects that are in the list itself. String objects have a __str__ or __repr__ method that represents them as the text, so that is what 'print' will output. Hope that helps, E. -- https://mail.python.org/mailman/listinfo/python-list
