Category: jython

Jython Tutorial PDF Version Quick Guide Resources Job Search Discussion Jython is the JVM implementation of the Python programming language. It is designed to run on the Java platform. Jython was created in 1997 by Jim Hugunin. It closely follows the standard Python implementation called CPython. Jython 2.7.0 was released in May 2015, which corresponds to CPython 2.7. This is an introductory tutorial, which covers the basics of Jython and explains how to handle its various modules and sub-modules. Audience This tutorial will be helpful for Java programmers who want to utilize important features of Python i.e. Simple Syntax, Rich Data Types and Rapid Application Development in Java code. This will also be useful for Pythonistas to import feature Java class library into the Python Environment. This tutorial is made to make the programmers comfortable in getting started with Jython and its various functions. Prerequisites Since Jython helps in integrating two very popular programming technologies namely Java and Python, a reasonable knowledge of both languages is required. Print Page Previous Next Advertisements ”;

Jython – Loops ”; Previous Next In general, statements in a program are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. There may be a situation when you need to execute a block of code several number of times. Statements that provide such repetition capability are called looping statements. In Jython, a loop can be formed by two statements, which are − The while statement and The for statement The WHILE Loop A while loop statement in Jython is similar to that in Java. It repeatedly executes a block of statements as long as a given condition is true. The following flowchart describes the behavior of a while loop. The general syntax of the while statement is given below. while expression: statement(s) The following Jython code uses the while loop to repeatedly increment and print value of a variable until it is less than zero. Live Demo count = 0 while count<10: count = count+1 print “count = “,count print “Good Bye!” Output − The output would be as follows. count = 1 count = 2 count = 3 count = 4 count = 5 count = 6 count = 7 count = 8 count = 9 count = 10 Good Bye! The FOR Loop The FOR loop in Jython is not a counted loop as in Java. Instead, it has the ability to traverse elements in a sequence data type such as string, list or tuple. The general syntax of the FOR statement in Jython is as shown below − for iterating_var in sequence: statements(s) We can display each character in a string, as well as each item in a List or Tuple by using the FOR statement as shown below − Live Demo #each letter in string for letter in ”Python”: print ”Current Letter :”, letter Output − The output would be as follows. Current Letter : P Current Letter : y Current Letter : t Current Letter : h Current Letter : o Current Letter : n Let us consider another instance as follows. #each item in list libs = [‘PyQt’, ”WxPython”, ”Tkinter”] for lib in libs: # Second Example print ”Current library :”, lib Output − The output will be as follows. Current library : PyQt Current library : WxPython Current library : Tkinter Here is another instance to consider. #each item in tuple libs = (‘PyQt’, ”WxPython”, ”Tkinter”) for lib in libs: # Second Example print ”Current library :”, lib Output − The output of the above program is as follows. Current library : PyQt Current library : WxPython Current library : Tkinter In Jython, the for statement is also used to iterate over a list of numbers generated by range() function. The range() function takes following form − range[([start],stop,[step]) The start and step parameters are 0 and 1 by default. The last number generated is stop step. The FOR statement traverses the list formed by the range() function. For example − Live Demo for num in range(5): print num It produces the following output − 0 1 2 3 4 Print Page Previous Next Advertisements ”;

Jython – Variables and Data Types ”; Previous Next Variables are named locations in computer’s memory. Each variable can hold one piece of data in it. Unlike Java, Python is a dynamically typed language. Hence while using Jython also; prior declaration of data type of variable is not done. Rather than the type of variable deciding which data can be stored in it, the data decides the type of variable. In the following example, a variable is assigned an integer value. Using the type() built-in function, we can verify that the type of variable is an integer. But, if the same variable is assigned a string, the type() function will string as the type of same variable. > x = 10 >>> type(x) <class ”int”> >>> x = “hello” >>> type(x) <class ”str”> This explains why Python is called a dynamically typed language. The following Python built-in data types can also be used in Jython − Number String List Tuple Dictionary Python recognizes numeric data as a number, which may be an integer, a real number with floating point or a complex number. String, List and Tuple data types are called sequences. Jython Numbers In Python, any signed integer is said to be of type ‘int’. To express a long integer, letter ‘L’ is attached to it. A number with a decimal point separating the integer part from a fractional component is called ‘float’. The fractional part may contain an exponent expressed in the scientific notation using ‘E’ or ‘e’. A Complex number is also defined as numeric data type in Python. A complex number contains a real part (a floating-point number) and an imaginary part having ‘j’ attached to it. In order to express a number in the Octal or the Hexadecimal representation, 0O or 0X is prefixed to it. The following code block gives examples of different representations of numbers in Python. int -> 10, 100, -786, 80 long -> 51924361L, -0112L, 47329487234L float -> 15.2, -21.9, 32.3+e18, -3.25E+101 complex -> 3.14j, 45.j, 3e+26J, 9.322e-36j Jython Strings A string is any sequence of characters enclosed in single (e.g. ‘hello’), double (e.g. “hello”) or triple (e.g. ‘“hello’” o “““hello”””) quotation marks. Triple quotes are especially useful if content of the string spans over multiple lines. The Escape sequence characters can be included verbatim in triple quoted string. The following examples show different ways to declare a string in Python. str = ’hello how are you?’ str = ”Hello how are you?” str = “””this is a long string that is made up of several lines and non-printable characters such as TAB ( t ) and they will show up that way when displayed. NEWLINEs within the string, whether explicitly given like this within the brackets [ n ], or just a NEWLINE within the variable assignment will also show up. “”” The third string when printed, will give the following output. this is a long string that is made up of several lines and non-printable characters such as TAB ( ) and they will show up that way when displayed. NEWLINEs within the string, whether explicitly given like this within the brackets [ ], or just a NEWLINE within the variable assignment will also show up. Jython Lists A List is a sequence data type. It is a collection of comma-separated items, not necessarily of the same type, stored in square brackets. Individual item from the List can be accessed using the zero based index. The following code block summarizes the usage of a List in Python. list1 = [”physics”, ”chemistry”, 1997, 2000]; list2 = [1, 2, 3, 4, 5, 6, 7 ]; print “list1[0]: “, list1[0] print “list2[1:5]: “, list2[1:5] The following table describes some of the most common Jython Expressions related to Jython Lists. Jython Expression Description len(List) Length List[2]=10 Updation Del List[1] Deletion List.append(20) Append List.insert(1,15) Insertion List.sort() Sorting Jython Tuples A tuple is an immutable collection of comma-separated data items stored in parentheses. It is not possible to delete or modify an element in tuple, nor is it possible to add an element to the tuple collection. The following code block shows Tuple operations. tup1 = (”physics”,”chemistry‘,1997,2000); tup2 = (1, 2, 3, 4, 5, 6, 7 ); print “tup1[0]: “, tup1[0] print “tup2[1:5]: “, tup2[1:5] Jython Dictionary The Jython Dictionary is similar to Map class in Java Collection framework. It is a collection of key-value pairs. Pairs separated by comma are enclosed in curly brackets. A Dictionary object does not follow zero based index to retrieve element inside it as they are stored by hashing technique. The same key cannot appear more than once in a dictionary object. However, more than one key can have same associated values. Different functions available with Dictionary object are explained below − dict = {”011”:”New Delhi”,”022”:”Mumbai”,”033”:”Kolkata”} print “dict[‘011’]: “,dict[”011”] print “dict[”Age”]: “, dict[”Age”] The following table describes some of the most common Jython Expressions related to Dictionary. Jython Expression Description dict.get(‘011’) Search len(dict) Length dict[‘044’] = ‘Chennai’ Append del dict[‘022’] Delete dict.keys() list of keys dict.values() List of values dict.clear() Removes all elements Print Page Previous Next Advertisements ”;

Jython – Using Java Collection Types ”; Previous Next In addition to Python’s built-in data types, Jython has the benefit of using Java collection classes by importing the java.util package. The following code describes the classes given below − Java ArrayList object with add() remove() get() and set() methods of the ArrayList class. Live Demo import java.util.ArrayList as ArrayList arr = ArrayList() arr.add(10) arr.add(20) print “ArrayList:”,arr arr.remove(10) #remove 10 from arraylist arr.add(0,5) #add 5 at 0th index print “ArrayList:”,arr print “element at index 1:”,arr.get(1) #retrieve item at index 1 arr.set(0,100) #set item at 0th index to 100 print “ArrayList:”,arr The above Jython script produces the following output − C:jython27bin>jython arrlist.py ArrayList: [10, 20] ArrayList: [5, 20] element at index 1: 20 ArrayList: [100, 20] Jarray Class Jython also implements the Jarray Object, which allows construction of a Java array in Python. In order to work with a jarray, simply define a sequence type in Jython and pass it to the jarrayobject along with the type of object contained within the sequence. All values within a jarray must be of the same type. The following table shows the character typecodes used with a jarray. Character Typecode Corresponding Java Type Z Boolean C char B byte H short I int L long F float D double The following example shows construction of jarray. Live Demo my_seq = (1,2,3,4,5) from jarray import array arr1 = array(my_seq,”i”) print arr1 myStr = “Hello Jython” arr2 = array(myStr,”c”) print arr2 Here my_seq is defined as a tuple of integers. It is converted to Jarray arr1. The second example shows that Jarray arr2 is constructed from mySttr string sequence. The output of the above script jarray.py is as follows − array(”i”, [1, 2, 3, 4, 5]) array(”c”, ”Hello Jython”) Print Page Previous Next Advertisements ”;

Jython – Installation ”; Previous Next Before installation of Jython 2.7, ensure that the system has JDK 7 or more installed. Jython is available in the form of an executable jar file. Download it from – https://www.jython.org/download.html and either double click on its icon or run the following command − java -jar jython_installer-2.7.0.jar An installation wizard will commence with which installation options have to be given. Here is the systematic installation procedure. The first step in the wizard asks you to select the language. The second step prompts you to accept the licence agreement. In the next step, choose the installation type. It is recommended to choose the Standard installation. The next screen asks your confirmation about your options and proceeds to complete the installation. The installation procedure might take some time to complete. After the installation is complete, invoke jython.exe from the bin directory inside the destination directory. Assuming that Jython is installed in C:jython27, execute the following from the command line. C:jython27binjython A Python prompt (>>>) will appear, in front of which any Python statement or Python script can be executed. Print Page Previous Next Advertisements ”;