Moving to Python from other Programming Languages

If you are already a programmer, Python could be the easiest to learn of all the languages you have encountered. It is pretty typical to learn the Python language while you are writing your first non-trival Python program! In other words, feel free to skip "Hello World" and move right to file administration, GUI programming, and exotic numerical analysis! I am exaggerating, I admit! But you will definately be much farther with Python during your first 3 days than you would be with any other language.

Here is an account of a programmer coming to Python and being extremely productive far sooner than he expected to be.

* ["http://www.linuxjournal.com/article.php?sid=3882" Eric S. Raymond "Why Python?"]

Significant Whitespace

The less said, the better. Python uses whitespace to signify end-of-line and code blocks. This will annoy you! But you will get used to it, as did thousands of programmers before you. You might even grow to like it.

comp.lang.python

Probably your most valuable Python resource, right after python.org. Spot Python luminaries in their native habitat! Don't be surprised to have your questions answered by the original programmer or the author of the book open on your desk! The best thing about comp.lang.python is how "newbie-friendly" the mail group is. You can ask any question and never get a "RTFM" thrown back at you.

Tips for "Thinking in Python"

(The phrase Thinking in Python was borrowed from the Bruce Eckel book of the same name. It is currently an online book, available for reading for free-as-in beer! ["http://www.mindview.net/Books/TIPython" Mindview Inc. Thinking in Python] This book is not meant for beginners to Python, however. It is the Python equivilant of Bruce Eckel's popular Thinking in C++ and Thinking in Java)

The following was taken from a post in comp.lang.python from Mel Wilson, which I thought well summarized good Python programming style for people coming from other languages. I also added some things I would have appreciated knowing during my first 3 days with Python.

* The docs at python.org are very, very good. Hold onto that wallet, you don't need a trip to the bookstore to learn Python!

* Scan the full list of built-in module names early on. Python is advertised as "batteries included", so knowledge of the built-in modules could make a 80 line program turn into a 8 line program.

* Learn Python slice notation, you will be using it a lot. I have this chart taped to my monitor:

Python indexes and slices for a six-element list.
Indexes enumerate the elements, slices enumerate the spaces between the elements.

Index from rear:    -6  -5  -4  -3  -2  -1      a=[0,1,2,3,4,5]    a[1:]==[1,2,3,4,5]
Index from front:    0   1   2   3   4   5      len(a)==6          a[:5]==[0,1,2,3,4]
                   +---+---+---+---+---+---+    a[0]==0            a[:-2]==[0,1,2,3]
                   | a | b | c | d | e | f |    a[5]==5            a[1:2]==[1]
                   +---+---+---+---+---+---+    a[-1]==5           a[1:-1]==[1,2,3,4]
Slice from front:  :   1   2   3   4   5   :    a[-2]==4
Slice from rear:   :  -5  -4  -3  -2  -1   :
                                                b=a[:]
                                                b==[0,1,2,3,4,5] (shallow copy of a)

* Lose the braces, as you know them, and most of the semicolons, obviously.

* Backslash can be used to allow continuing the program line past a carriage-return, but you almost never have to use it. Python is smart enough to do the right thing when it sees an open bracket, a comma separated list, and a carriage-return.

* Strings are immutable. Whenever you think you have changed a string, remember that you really created a new string.

* Where you would use <vector T>, use lists, or tuples, that is [] or (). Where you would use <map T1, T2>, use dictionaries, that is {} .

* The semantics of iterators is available, but most of the syntax goes away. for item in alist: iterates over all the items in alist, one by one .. where alist is a sequence, i.e. a list, tuple, or string. To iterate over a sublist, use slices: for item in alist[1:-1]: does as above, but omits the first and last items.

* For trickier iterations, read and re-read the Library doc on the topic of general-purpose functions. There are some functions that apply to sequences: map, filter, reduce, zip. that can work wonders. Hidden somewhere under the documentation for sequences there is a description of string methods that you'll want to read.

* Hidden under the docs for 'Other Types' are the descriptions of all the file methods. There are no iostreams per se, but the class method str can get some of the effect for your own classes, and there are surely other angles I haven't thought of.

* Forget polymorphism. You can define a function, and call it with anything you want, but if it has to behave differently for different type operands, you have to use the run-time type identification type function explicitely within the single definition of the function. Default arguments to functions are just as powerful a tool as in C++.

* In class definitions the equivalents of operator methods are covered in a chapter in the Python Language Reference. (Look for the double-underscore methods like cmp, str, add, etc.)

* In C, the gotcha for new users is probably about pointers; they're tricky and they can't be avoided. The gotchas in Python are situations when you use different references to a single object, thinking you are using different objects. I believe the difference between mutable and immutable objects comes into play. I have no clear answers here .. I still get caught once in a while .. keep your eyes open.

* Read the Tutorial once, skim the Library Reference .. at least the table of contents, then skim the Language Reference and you will probably have encountered everything you need.