Re: New to Python: Features
From: Dan Bishop (danb_83_at_yahoo.com)
Date: 10/05/04
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Date: 5 Oct 2004 01:43:18 -0700
Richard Blackwood <richardblackwood@cloudthunder.com> wrote in message news:<mailman.4286.1096945096.5135.python-list@python.org>...
> Hi, I'm new to Python and I'd like to know if Python has the following
> support: *please answer to each individually, thanks*
Most of your questions are answered at http://docs.python.org/
> 1. Multi line comments
No. But multi-line docstrings are supported.
> 2. Functions as variables:
> a. functions can be stored in variables, passed as arguments to
> other functions, and returned as results.
Yes.
>>> def deriv(f, x, delta=1e-8):
... "Centered difference approximation of f'(x)"
... return (f(x + delta) - f(x - delta)) / (2 * delta)
...
>>> deriv(lambda x: x * x, 2)
3.9999999756901161
> 3. Function nesting with proper lexical scope (i.e. closures)
Yes.
> 4. Operator overloading (inc. the ability to define new operators)
Yes. This is done by defining the special methods __add__, __mul__,
etc.
> 5. Can I do this? print("Hello " .. "World") --> Hello World
If ".." is supposed to be the string concatenation operator, then yes.
>>> print "Hello " + "World!"
Hello World!
> 6. Constructors
Yes. They're defined like this:
class MyClass:
def __init__(self, arg1, arg2):
# ...
and called like this:
x = MyClass(arg1, arg2)
> 8. "Repeat-Until" as in :
> repeat
> line = os.read()
> until line ~= ""
> print(line)
There isn't a special syntax for posttest loops. You have to write
them like
while True:
line = os.read()
if not line:
break
print line
> 10. Can I call an object's method as object:method(arg) and have that
> translate into object.method(object, arg)
>>> class MyClass:
... def foo(self, arg):
... pass
...
>>> m = MyClass()
>>> m.foo(0)
>>> MyClass.foo(m, 0)
> 11. Can I make dynamic statements and nature like with eval() in Javascript?
Yes.
>>> x = 1; y = 2
>>> z = eval("x + y")
>>> exec "print z"
3
> 12. Can I make calls to a function with a varying number of arguments?
Yes.
>>> def func(fixedArgA, fixedArgB, *args):
... print "called with", 2 + len(args), "arguments"
...
>>> func(1, 2, 3, 4)
called with 4 arguments
>>> func(1, 2, 3, 4, 5, 6)
called with 6 arguments
> 13. Named arguments
Yes.
>>> datetime.date(month=10, day=5, year=2004)
datetime.date(2004, 10, 5)
> 14. Tables with built-in methods for manipulation such as sort, etc.
Try the built-in "list" type. Also, "dict".
> 15. Table filters
I'm not quite sure what you're asking. Do you mean something like
>>> [n for n in xrange(2, 20) if isprime(n)]
[2, 3, 5, 7, 11, 13, 17, 19]
?
> 15. Proper Tail Call (otherwise known as Proper Tail Recursion)
No.
> 16. The ability to call a function without brackets
Fortunately, no.
> 17. Is the Python interpreter a JIT? Does it have a bytecode? Is it as
> fast as Java?
For the standard interpreter: No. Yes. No.
But try Psyco (psyco.sourceforge.net).
> 21. May modules be stored in variables, passed to and produced from
> functions, and so forth?
Yes.
>>> import sys
>>> import os
>>> modules = [sys, os]
>>> modules[1].getcwd()
'/home/dan'
> 22. Is the self parameter hidden from me as a programmer? Can I
> hide/unhide it as I wish?
No.
> 25. A fully implemented .NET counterpart (I should be able to write
> Python scripts for both with the same code)
It's not fully implemented yet, but there is a .NET version
(http://www.ironpython.org).
> 33. Function/Method overloading
No, but it can often be simulated by default parameters, or by
"isinstance" checks.
> 34. In pure Python, can I change and add new constructs to the Python
> syntax?
No.
> 43. Embedding variables in strings like: print "Hello, World. Time:
> #{Time.now}"
No, but this can be written almost as easily using the % operator.
>>> print "Hello, World. Time: %s" % datetime.datetime.now()
Hello, World. Time: 2004-10-05 03:12:14.750796
or
>>> now = datetime.datetime.now()
>>> print "Hello, World. Time: %(now)s" % locals()
Hello, World. Time: 2004-10-05 03:14:01.111879
> 44. Case or Switch statements with functionality as such:
> case score
> when 0...40
> puts "Horrible!"
> when 40...60
> puts "Poor"
> when 60...80
> puts "You can do better!"
> when 80...95
> puts "Now that's acceptable"
> when 95..100
> puts "That the best you can do? j/k"
> else
> puts "Didn't take the test?"
> end
Python does not have a switch/case construct. Your example would
normally be written as an if...elif...else ladder.
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