cuckookernel/pythontojulia.md

## pythontojulia.md

      
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              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
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
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
Python	Julia
f = open( "file.txt" )	f = open( "file.txt")
for line in f	for line in eachline( f )
f.close()	close( f )
Python	Julia
`raise excetion`	`throw( exception )`
RuntimeError( "msg" )	(?) ErrorException( "msg" )
	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