Programming in Python vs. programming in Java

Question

I\'ve been writing Java for the last couple of years , and now I\'ve started to write in python (in addition).

The problem is that when I look at my Python code it

Answer 1

1) Python supports many (but not all) aspects of object-oriented programming; but it is possible to write a Python program without making any use of OO concepts.

1) Java supports only object-oriented programming.

2) Python is designed to be used interpretively. A Python statement may be entered at the interpreter prompt

(>>>)

, and will be executed immediately. (Implementations make some use of automatic compilation into bytecodes (.pyc files).

2) Programs written in Java must be explicitly compiled into bytecodes (.class files), though an IDE may do this automatically in a way that is transparent to the user. Java does not support direct execution of statements - though there are tools like Dr. Java that support this.

3) Python is dynamically typed: • A variable is introduced by assigning a value to it. Example:

someVariable = 42

• A variable that has been assigned a value of a given type may later be assigned a value of a different type. Example:

someVariable = 42
someVariable = 'Hello, world'

3) Java is

statically typed

: • A variable must be explicitly declared to be of some type before assigning a value to it, though declaration and assignment may be done at the same time. Examples:

int someVariable;
int someVariable = 42;

• A variable that has been declared to be of a particular type may not be assigned a value of a different type.

4) Python supports the following built-in data types: Plain integers (normally 32-bit integers in the range -2147483648 through 2147483647). • Long integers (size limited only by memory size of the machine running on) • Booleans (False and True). • Real numbers. • Complex numbers. In addition, Python supports a number of types that represent a collection of values - including strings, lists, and dictionaries.

4) Java has two kinds of data types: primitive types and reference types. Java supports the following primitive data types: • byte - 8-bit integers • short - 16-bit integers • int - 32-bit integers • long - 64-bit integers (Java also supports a class java.math.BigInteger to represent integers whose size is limited only by memory) • float - 32-bit real numbers. • double - 32-bit real numbers. • boolean - (false and true). • char - a single character. In addition, Java supports arrays of any type as the reference types, and the API includes the class String and a large number of classes used for collections of values.

5)

Python is line-oriented:

statements end at the end of a line unless the line break is explicitly escaped with . There is no way to put more than one statement on a single line. Examples: this is a statement this is another statement this is a long statement that extends over more \ than one line

5)

Statements in Java always end with a
semicolon (;)

. It is possible for a statement to run over more than one line, or to have multiple statements on a single line. Examples: this is a statement; this is another statement; this is a long statement that extends over more than one line; a statement; another; another;

6)

Python comments begin with #

and extend to the end of the line. Example:

This is a comment

A new statement starts here

6) Java has two kinds of comments. A comment beginning with // extend to the end of the line (like Python comments). Comments can also begin with /* and end with */. These can extend over multiple lines or be embedded within a single line. Examples:

// This is a comment
A new statement starts here
/* This is also a comment */
/* And this is also a comment, which is
 long enough to require several lines
 to say it. */

Statement starts /* comment */ then continues

7) Python strings can be enclosed in either single or double quotes (' or ""). A character is represented by a string of length 1. Examples:

'This is a string'
"This is also a string" # Equivalent
'c' # A string
"c" # An equivalent string

Python uses the following operators for constructing compound boolean expressions:

and, or and not. Example:
not(x > 0 and y > 0) or z > 0

7) Java strings must be enclosed in double quotes (""). A character is a different type of object and is enclosed in single quotes ('). Examples:

"This is a String"
'c' // A character, but not a String
Java uses the following operators for
constructing compound boolean expressions:
&&, ||, ! and ^ (meaning exclusive or)
Example:
! (x > 0 && y > 0) || z > 0 ^ w > 0

8) In Python, the comparison operators

(>, <, >=, <=, == and !=) can be applied to numbers

, strings, and other types of objects), and compare values in some appropriate way (e.g. numeric order, lexical order) where possible.

8) In Java, most of the comparison operators ( >, <, >=, and <=) can be applied only to primitive types. Two (== and !=) can be applied to any object, but when applied to reference types they test for same (different) object rather than same (different) value.

9) There is no universally-accepted Python convention for naming classes, variables, functions etc.

9) By convention, most names in Java use mixed case. Class names begin with an uppercase letter; variable and function names begin with a lowercase letter. Class constants are named using all uppercase letters with underscores. Examples: AClassName aVariableName aFunctionName() A_CLASS_CONSTANT

10) Python definite looping statements have the form for variable in expression: Example:

for p in pixels:
 something

10) Java has two kinds of definite looping statements. One has the form

for (variable in collection) Example:
for (p in pixels)
 something;

11) Python uses the built-in function range() with for to loop over a range of integers. Examples:

for i in range(1, 10)
 something
(i takes on values 1, 2, 3, 4, 5, 6, 7, 8, 9)
for i in range(1, 10, 2)
 something
(i takes on values 1, 3, 5, 7, 9)

11) Java uses a different form of the for to loop over a range of integers. Examples:

for (int i = 1; i < 10; i ++)
 something;
(i takes on values 1, 2, 3, 4, 5, 6, 7, 8, 9)
for (int i = 1; i < 10; i += 2)
 something;
(i takes on values 1, 3, 5, 7, 9)

12) Python conditional statements have the form if condition: and an optional else part has the form else:. The form elif condition: is allowed as an alternative to an else: immediately followed by an if. Examples:

if x < 0:
 something
if x < 0:
 something
else:
 something different
if x < 0:
 something
elif x > 0:
 something different
else:
 yet another thing

12) Java conditional statements have the form if (condition) and an optional else part has the form else (no colon) There is no elif form - else if is used directly. Examples:

if (x < 0)
 something;
if (x < 0)
 something;
else
 something different;
if (x < 0)
 something;
else if (x > 0)
 something different;
else
 yet another thing;

13) The scope of a Python conditional or looping statement is denoted by indentation. (If multiple lines are to be included, care must be used to be sure every line is indented identically). Examples:

if x < 0:
 do something
do another thing regardless of the value of x
if x < 0:
 do something
 do something else
 do yet a third thing
do another thing regardless of the value of x

13) The scope of a Java conditional or looping statement is normally just the next statement. Indentation is ignored by the compiler (though stylistically it is still highly desirable for the benefit of a human reader). If multiple lines are to be included, the scope must be delimited by curly braces ({ , }). (Optionally, these can be used even if the scope is a single line.) Examples:

if (x < 0)
 do something;
do another thing regardless of the value of x;
if (x < 0)
do something; // Bad style-don't do this!
do another thing regardless of the value of x;
if (x < 0)
{
 do something;
 do something else;
 do yet a third thing;
}
do another thing regardless of the value of x;
if (x < 0)
{
 do something;
}
do another thing regardless of the value of x;

Answer 2

This is useful if you want to understand how to code to python in a more pythonic or correct way: http://www.python.org/dev/peps/pep-0008/

Answer 3

If you are new to Python and coming from Java (or C#, or other similar statically typed OO language), these classic articles from PJ Eby and Ryan Tomayko are necessary reading:

• Python Is Not Java (PJE)
• Java is not Python, either (PJE)
• Python Interfaces are not Java Interfaces (PJE)
• The Static Method Thing (Tomayko)
• Getters/Setters/Fuxors (Tomayko)

Answer 4

You might consider immersing yourself in the Python paradigms. The best way is to first know what they are then explore the best practices by reading some literature and reviewing some code samples. I recommend Learning Python by Mark Lutz; great for beginners and advanced users.

You'll do yourself a great injustice if you program with Python and fail to leverage all of the built-in, developer-friendly, Pythonic syntax.

As my French teacher used to say, "French isn't just English with different words."

Answer 5

You could post your code at Refactor my code to see if someone can show you a more Pythonic way to do it.

Answer 6

Definitely not a panacea but I think you should try some code golf in Python. Obviously nobody should write "golfed" code IRL, but finding the most terse way to express something really forces you to exploit the built in functionality of the language.