Jython Quick References

Table 1. Summary of Jython data types

Type	Comment	Example
Null	An undefined value (like null in the Java language).	None
Integer	A normal (int in the Java language) or long (BigInteger in the Java language) integer number.	-1 0 100 -1L 1000000000000000000000000000000000000000000001L
Float	A fractional or exponential (like double in the Java language) number.	1.0 -1e6 0.000001e-10 1E11
Complex	A pair of floats supporting complex arithmetic.	1j -10J 2-3j 1e6j
String	An immutable sequence of characters. There is no character type (use one character strings instead).	"a string" 'a string' """a long (possibly multi-line) string""" '''another (possibly multi-line) long string''' r'''^xxx(.*?)\.yyy(.*?)\.zzz(.*?)\.$''' 'x' "y" '\n' "\\"
Range	An immutable sequence of integers.	range(10) range(10,0,-1) xrange(1,100000,10)
Tuple	An immutable sequence of any type (like java.util.Collections.unmodifiableCollection(someList)).	() (1,) (1,2,3) (1, "mixed", 2, "tuple") ((1,2),(3,4))
List	A mutable sequence of any type (like java.util.ArrayList).	[] [1] [1,2,3] [1, 'mixed', 2, 'list'] [[1,2],[3,4]]
Map	A mutable collection of items (name/value pairs) (like java.util.Map). Names must be immutable and unique; values may be None.	{} {1:'one',2:'two',3:'three'} {"one";1, "two":2, "three":3} {"x":1, "ints":(1,2,3), "name":{"first":"Barry", last":"Feigenbaum"}}
Boolean	A true/false value based on other types.	false - 0 or empty: None 0 0.0 () [] true - non-0, not empty: 1 -1 0.0001 [1] [1,2,3] {"greeting":"Hello!"}
Function	Any function. Functions do not need to be members of classes.	lambda x: x > 0 def isPositive(x): return x > 0 def addem(x,y,z): return x + y + z
Class	Any class. Classes are namespaces for class attributes and functions (called methods).	class MyClass: x = 1 y = 2 class subclass(superClass): def method1(self): ... def method2(self, arg1, arg2): ...
Module	A source file (and namespace) that contains variable, function and/or class definitions.	Any .py file that defines importable variables, functions and/or classes. If it does not define any of these then it is just called a script.

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Statement types

Jython provides the statement types summarized in Table 2.

Table 2. Summary of Jython statement types

Statement	Comment	Examples
Expression	Any expression. The results are discarded. Often used for their side effects.	(1 * 2) ** 3 / 4 "string"[2:] == "ring" someFunction(1, 2, 3)
Assignment	Assigns an expression to a target.	x = 3 x = f(1,32,3) * 10 + x list[1:3] = [7, 8, 9 , 10]
Augmented Assignment	Updates a target with an expression.	x *= 100 s += "…"
Unpacking Assignment	Assigns elements of a sequence to multiple targets; very convenient for access to tuple and list members. Note that the expression 1,2,3 is a short form of (1,2,3).	x,y,z = 1,2,3
Multiple Assignment	Assigns the same expression to multiple targets.	z = y = z = 10
Pass	No operation.	pass
If If/Else If/Elif/Else	Conditional processing.	if x < 0: x = -x if x == 3: print "It's three!" if x == 1: ... elif x == 2: ... elif x == 3: ... else: print "Bad value " + x
While	Looping over a condition.	x = 10 while x > 0: print x x -= 1
For	Iterates over a sequence. Use range to iterate over a numeric sequence.	for i in range(10): print i for c in "A string": print c for i in (10, "Hello", 1e6): print func(i)
Continue	Advances to the next loop (while/for) iteration.	for i in range(10): if not testOk(i): continue :
Break	Exits a loop (while/for)	for i in range(10): if testBad(i): break :
Delete	Removes a variable or sequence element(s) or class attribute.	del x del list[3:5] del x.attr1
Global	Declares a reference to a global value; used in functions.	x,y,z = 0,1,2 def f(a,b,c): global x,y,z :
Print	Prints expression(s) to a stream.	print "Hello World!" print "Hello","World!" print "Hello" + ' ' + "World!" msg = "Name: %(last)s, (first)s" data = {'last':"Feigenbaum", 'first':"Barry"} print >>out, msg % data
Assert	Asserts a condition is true.	def process(v): assert v > 0, "Illegal value %i" % v :
Import	Imports all or part of a module.	import sys from sys import argv from javax import swing from java.util import Map
Execute	Executes a string/file as a subprogram. There is also a related function, exec, that executes a constructed string and returns its result. This support allows you to dynamically create programs.	globals = {'x':1, 'y':2, 'z':3} locals = {'list':(1,2,3)} code = "print x, y, z, list" exec code in globals, locals
Try/Except	Executes code within an exception handler.	try: x = int(string) except ValueError, e: x = 0
Try/Finally	Executes code with a cleanup routine.	f = open("test.dat") try: lines = f.readlines() finally: f.close()
Raise	Creates and throws an exception.	def factorial(x): raise ValueError, "x must be > 0" :
Define	Defines a function; arguments may be optional and/or keywords; Functions are generic which allows for very flexible programming.	def f(x,y=2,z=10): return x+y+z q = f(1,2) + f(3) + f(4,5,6) s = f("a","b","c")
Return	Returns from a function with an optional value.	return 10
Class	Defines a class (a container for attributes and methods) .	class X: pass class MyClass(SomeClass): pass

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