Python to Julia Quick translation / conversion reference Guide

pythontojulia.md

A quick and dirty syntax translation / conversion reference guide to ease the transition between Python and Julia. This is not meant as a reference to the language. For that you should read the manual.

Some important differences

• Arrays in Julia are indexed starting from 1.
• In Julia classes (i.e. types) don't own methods. Methods are implementations of generic functions and are invoked in a "static style", i.e. instead of Python's str1.rstrip(), we will have rstrip( str1 ), instead of file1.close(), close( file1 ).

Some important similarities.

Core

Getting around: All objects

Python	Julia	Comments
True	true
False	false
None	nothing
type( obj )	typeof( obj )
{}	Dict{KeyType,ValueType}()
elif	elseif
lambda x, y : y + x * 2	(x,y) -> y + x * 2
"string %s interpolation %d" % ( str1, i1)	"string $str1 interpolation $i1 "	You can interpolate arbitrary expressions by enclosing them in braces, as in "${x+y}"
xrange(10,4,-2)`	10:-2:4
range(10,4,-2)	[10:-2:4]	Do this only if you really have to, as it will consume memory proportional to the length of the range
id( obj )	object_id( obj )
raise excetion	throw( exception )
obj.fun( x, y)	fun( obj, x, y) with Lazy.jl @> obj f(x,y)	## Basic String operations

Python	Julia
str1 + str2 + str2	string( str1, str2, str3 )
len( str1 )	length( str1 )
str1.rstrip()	rstrip( str1 )
str1.startswith( x )	??? write your own such as the one in pytojul.jl

Regular expressions

Python	Julia
m = re.match( r"(\d+):(\d+)", mystr )	m = match( r"(\d+):(\d+)", mystr )
m is not None	m != nothing
arr = m.groups()	arr = m.captures

File processing

Python	Julia
f = open( "file.txt" )	f = open( "file.txt")
for line in f	for line in eachline( f )
f.close()	close( f )

Exceptions

(http://julia.readthedocs.org/en/latest/manual/control-flow/#exception-handling)

Python	Julia
raise excetion	throw( exception )
RuntimeError( "msg" )	(?) ErrorException( "msg" )

pytojul.jl

module pytojul.jl 

export startswith

function startswith( x::ASCIIString, y::ASCIIString )
# Disclaimer: This function is still buggy. Please help me find the bug...

    if  length(y) > length(x)
        return false
    else
        for i = 1 : length(y)
           if x[i] != y[i]
               return false
           end
        end
        return true
    end
end

end #module

Now there is a startswith function in Base.