# Re: Torn in two - Pythonist

**URL:** <https://www.ruby-forum.com/t/re-torn-in-two-pythonist/75576>\
**Category:** Ruby\
**Created:** [March 2, 2006, 2:47am UTC](https://www.ruby-forum.com/t/re-torn-in-two-pythonist/75576 "2006-03-02T02:47:53Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Christopher\_Dunn](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/6f9a4e/32.png) [@Christopher\_Dunn](https://www.ruby-forum.com/u/Christopher_Dunn)\
**Post date:** [March 2, 2006, 2:47am UTC](https://www.ruby-forum.com/t/re-torn-in-two-pythonist/75576/1 "2006-03-02T02:47:53Z")

</div>

Reference:  
[http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/178606](http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/178606)

I’m a recent convert myself. I was convinced by this blog that I found  
via  
O’Reilly:

> **[O'Reilly Media - Technology and Business Training](https://www.oreilly.com)**
>
> Gain technology and business knowledge and hone your skills with learning resources created and curated by O'Reilly's experts: live online training, video, books, our platform has content from 200+ of the world's best publishers.

I will finish a project at work, where I use a powerful, pre-existing  
Python  
interface to a C++ library. Then, sadly, I’m done with Python (as soon  
as  
Ruby2.0 is out, fixing some annoyances).

The best place to look is The Ruby Way. There is a 20-page appendix for  
Python converts, and another for Perl. Also read the 50 pages of Chapter  
1,  
especially the gotchas under “Things to Remember”. That’s really all you  
need, coming from either Python or Perl. (It will take some time to  
understand blocks and continuations, but you don’t have to use them.)

There is a list of some differences with Python in [ruby-talk:_01528_]  
_ruby  
\<=\> python_  
[http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/1528](http://blade.nagaokaut.ac.jp/cgi-bin/vframe.rb/ruby/ruby-talk/1528)

By far, the biggest gotcha is that 0 does not equal false. Another is  
that  
some mutating functions return nil when they change nothing, so you get  
unexpected exceptions from strung-together expressions like:  
foo().gsub!().bar()

The number of similarities is amazing, partly because Ruby and Python  
borrow  
from similar sources, and sometimes each other. E.g.

- raise RuntimeError, msg
- yield
- def/class
- for i in list
- [1,2,3]
- \*args (and keyword args in Ruby2.0)
- default function parameters
- ‘.’ for method calls

I’ve put together my own table of some differences. Semicolons indicate  
related lines. Otherwise, separate statements represent other ways to do  
the  
same thing. (Hopefully, the HTML formatting works.)

Python  
Ruby  
type(42) → \<type ‘int’\>  
42.class → Fixnum  
1e6  
1.0e6  
type(1e6) → \<type ‘float’\>  
1.0e6 # not 1.e6

1.0e6.class → Float  
“Hello, %s” %(name)  
‘Hello, %s’ %s(name)  
type(‘’) → \<type ‘str’\>  
“Hello, #{name}” # not single quotes

‘’.class → String  
“Hello\backslash \n newline”  
‘Hello\backslash \n no newline’  
print func(x)  
puts func x  
puts(func(x))  
puts func(x)  
puts(func x)  
a = 4  
A = 5  
a = 4 # lower case  
class C: pass  
class c: pass  
class C end # upper case  
NOT\_CONST = 5;  
NOT\_CONST = 6  
CONST = 5;  
CONST = 6 → warning (upper case)  
var  
global: $var  
instance: @var  
classvar: @@var  
None  
nil  
False, None,  
[], {}, 0, ‘’  
false, nil, FALSE, NIL # all others are true  
arr = []  
arr = list()  
arr = ()  
arr = tuple()  
arr = []  
arr = Array.new

# no tuples, but …

arr = [1,2,3].freeze  
assoc\_arr = {}  
assoc\_arr = dict()  
assoc\_arr = {}  
assoc\_arr = Hash.new  
a = {};  
a[42] → IndexError  
a = {};  
a[42] → nil  
a = Hash.new(2001);  
a[42] → 2001;  
a.keys → []  
if x:  
do\_something()  
elif y:  
do\_something\_else()  
else:  
do\_anything()  
if x # no colons  
do\_something  
elsif # Note spelling  
do\_something\_else  
else  
do\_anything  
end # Must have

do\_something if x # no ‘end’ here  
while x and y:  
do\_something  
while x and y  
do\_something  
end

begin  
do\_something  
end while false

# Here, do\_something occurs once!

# (Matz deprecates this usage.)

do\_something while false

# Here, do\_something never happens.

result = os.popen(command).read()  
result = `#{command}`  
results = IO.popen(command, ‘r’).gets  
re.compile(stuff)  
Regexp.new(stuff)  
/stuff/  
%r{stuff}  
regex.search(s)  
s ~= regex

# returns position

# Note: 0 is not false

return x  
return x  
x # ‘return’ is not needed  
class Dog(Animal, Friend):  
normal = 0  
def **init** (self):  
self.happiness = Dog.normal  
def wag(self, speed):  
self.happiness = speed  
class Dog \< Animal  
@@normal = 0  
def initialize()  
@happiness = @@normal  
end  
def wag(speed)  
@happiness = speed  
end  
end  
try:  
try:  
do\_it()  
finally:  
undo\_it()  
except RuntimeError, exception:  
print exception  
except:  
print “Unexpected”  
else:  
print “No exception raised.”  
begin  
do\_it()  
rescue RuntimeError =\> exception  
puts exception  
rescue exc  
puts “Unexpected”, exc  
else  
puts “No exception raised.”  
ensure  
undoit()  
end