On 7/26/2011 8:01 PM, rantingrick wrote:
============================================================ The "Fundamental Five" built-in functions ============================================================ There are quite a few helpful built in functions provided to the python programmer however in my mind five of them are the most important to Python noobs. The "fundamental five" i call them. I believe you should not do anything with Python until you are completely familier with these five because most of the bugs and mis- understanding a new user experiences can be solved by using these five functions. ============================================================ -------------------------------------------------- 1. help() -------------------------------------------------- http://docs.python.org/py3k/library/functions.html#help
help() with no args puts one into a special help mode to get info on various topics. help(obj) gets help on that object. I do not do the former much, but I increasingly use the latter.
-------------------------------------------------- 2. dir() -------------------------------------------------- http://docs.python.org/py3k/library/functions.html#dir Python has name spaces. Name spaces are awesome. Name spaces keep code from clashing with other code. The dir() function will list the currently defined names in the current namespace. If your getting NameErrors check the name space with dir() function.
I use this constantly.
-------------------------------------------------- 3. repr() -------------------------------------------------- http://docs.python.org/py3k/library/functions.html#repr Most new user think that printing an object to stdout is all they'll ever need. However when you call print -- or sys.stdout.write(object) -- you are only seeing a "friendly" version of the object.
This mostly applies to strings, which *do* have 2 printed versions. It is occasionally very important for debugging string problems.
Printing collections alreays used repr() for members of the collection.
-------------------------------------------------- 4. type() -------------------------------------------------- http://docs.python.org/py3k/library/functions.html#isinstance Ever had a TypeError? Ever had some object you were just sure was one type but is not behaving like that type? Then check it's type for Pete's sake! Even experienced programmers (of many languages) suffer from TypeErrors (be them subtle or not) because the type of an object cannot be inferred simply by looking at it's identifier. So when something ain't right, skip the tripe, and check the type! -------------------------------------------------- 5. id() -------------------------------------------------- http://docs.python.org/py3k/library/functions.html#id Ah yes, another source of frustration is the old "identical twin" syndrome (or in the worst forms; multiplicity syndrome!). Yes, on the surface that list of lists looks as if it contains unique elements HOWEVER you keep getting strange results. How are you going to find the problem? Hmm? Never fear my confused new friend, by comparing the ids of two objects you can know if they are actually the same or different. If the id is the same, the objects are the same.
This is the most dangerous of the builtins, as it sometimes mislead newbies into 'discovering' non-existent 'bugs'. The main point is that the id of immutable objects is mostly an irrelevant implementation detail, while the id of mutables may be critical. Lists of lists is a particular area where id() is really useful.
-- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
