Getting Started with Julia for Pythonista

It's a story that feels like it's decocted ... [Faster] than Python (http://julialang.org/benchmarks/), it's written closer to Python, and it's the most noticeable language in my life these days.

This time, I will introduce the difference in syntax that Pythonista needs to remember when using Julia by comparing Python and Julia.

Click here to build Julia's environment (http://julialang.org/downloads/)

Basic knowledge

The code is indented for clarity, but the indentation is not related to behavior.

julia

for n = 1:10
println(n)
end

If you write in one line, you need ;.

julia

for n = 1:10;println(n);end

Also, the index of list is from ** 1 **, not from 0.

julia

julia> List = [0, 1, 2]
3-element Array{Int64,1}:
 0
 1
 2

julia> println(List[1])
0

Hello World!

python

print "Hello World!"

julia

println("Hello World!")

for Loop statements

python

for i in range(10):
	print i

julia

for n = 0:9
	println(n)
end

If statements

python

hoge = "hoge"
if hoge[0] == 'h' and hoge[1:] == "oge":
	print "hoge is hoge"
elif hoge == "huge" or hoge == "hige":
	print "hoge is huge or hige"
else:
	print "hoge is", hoge

In JuliaandIs&&、orIs||is.

julia

hoge = "hoge"
if hoge[1] == 'h' && hoge[2:4] == "oge"
	println("hoge is hoge")
elseif hoge == "huge" || hoge == "hige"
	println("hoge is huge or hige")
else
	println("hoge is ", hoge)
end

It works with hoge [2:], but * WARNING: deprecated syntax "x [i:]". * Appears, so I write hoge [2: 4].

Exception Handling (Try-Except)

python

List = [0, 1, 2]
try:
	print List[3]
except IndexError as e:
	print e

julia

List = [0, 1, 2]
try
	println(List[4])
catch e
	if isa(e, BoundsError) # "BoundsError"Says in python"IndexError"is
		println(e)
	end
end

Functions

python

def huge(x, y):
	z = x + y
	return z

julia

function huge(x, y)
	x + y
end

Or

julia

function huge(x, y)
	z = x + y
	return z
end

Anonymous Functions

python

z = lambda x, y : x + y 
z(1, 2)

julia

z = (x, y) -> x + y
z(1, 2)

Working with Files

Read

python

with open("output.txt") as f:
	for line in f:
		print line.rstrip() #Removed line feed code to match Julia output

julia

open("output.txt") do f
	lines = readlines(f)
	for line in lines
		print(line) #Julia print()Does not contain a line feed code
	end
end

Or

julia

open("output.txt") do f
	for line in eachline(f)
		print(line)
	end
end

Write

python

with open("output.txt", "w") as f:
	for i in range(10):
		f.write(str(i) + "\n")

julia

open("output.txt", "w") do f
	for n = 0:9
		write(f, string(n)"\n")
	end
end

List complemention

python

[[n**i for n in range(10)] for i in range(5)]

julia

[[n^i for n = 0:9] for i = 0:4]

Create a list of each element plus 10

python

[n+10 for n in range(10)]

julia

10+[0:9]

Detailed story

printf

python

Integer = 2
String  = "hoge"
print("Integer: %d String: %s" % (Integer, String))

julia

Integer = 2
String  = "hoge"
@printf "Integer: %d String: %s" Integer String

strip()

python

>>> "hoge\n".rstrip()
'hoge'

julia

julia> rstrip("hoge\n", '\n')
"hoge"

Other good points of Julia

infix form

julia

julia> +(10, 20, 30)
60

julia> *(10, 20, 30)
6000

Or

julia

julia> f = +
+ (generic function with 117 methods)

julia> f(10, 20, 30)
60

julia> f = *
* (generic function with 115 methods)

julia> f(10, 20, 30)
6000

inverse divide

julia

julia> 1/3
0.3333333333333333

julia> 3\1
0.3333333333333333

Function chaining

julia

julia> [0:5] |> x -> x.^x |> sum
3414

reference

Julia Documentation