Python equivalent of Java .jar files

Problem
In Java, you can distribute your project in JAR format. It is essentially a ZIP file with some metadata. The project can be launched easily:

$ java -jar project.jar

What is its Python equivalent? How to distribute a Python project (with several modules and packages) in a single file?

Solution
The following is based on this post, written by bheklilr. Thanks for the tip.

Let’s see the following project structure:

MyApp/
    MyApp.py          <--- Main script
    alibrary/
        __init__.py
        alibrary.py
        errors.py
    anotherlib/
        __init__.py
        another.py
        errors.py
    configs/
        config.json
        logging.json

Rename the main script to __main__.py and compress the project to a zip file. The extension can be .egg:

myapp.egg/             <--- technically, it's just a zip file
    __main__.py        <--- Renamed from MyApp.py
    alibrary/
        __init__.py
        alibrary.py
        errors.py
    anotherlib/
        __init__.py
        another.py
        errors.py
    configs/
        config.json
        logging.json

How to zip it? Enter the project directory (MyApp/) and use this command:

zip -r ../myapp.egg .

Now you can launch the .egg file just like you launch a Java .jar file:

$ python myapp.egg

You can also use command-line arguments that are passed to __main__.py.

Python vs Java in relation to logos

Emanuel Couto explains the difference between Python and Java, comparing the logos of the two languages:

“I read almost all comments and I there is one point that all of you missed! The logo is important for productivity!

The Python logo is obviously a snake. The name of the language, however, was based on Monty Python. So what this means is that you are going to have good laughs when the python bytes you. Specially when the code is too long to debug or understand.

The Java logo is a cup of coffee. What this means is that you are going to need coffee when programming in Java or you will fall asleep. In fact you are going to need loads of coffee when your code is near production stage. BTW I don’t drink coffee, so my job is twice as hard.

Jython is when you give coffee to a snake. Jython users are people that drank toomuch coffee and over time it doesn’t have any effect anymore. Since the python needs to sleep, the solution is giving coffee so that Java programmers can also have laughs at late hours of the day.

And that folks is a true story.” (source)

Print colored text in terminal

Problem

In the terminal, you want to print some texts in colored mode. For instance, warnings in red.

Solution

There is a module for this task called termcolor. You can install it with this command:

sudo pip install termcolor

Or, simply download it and put termcolor.py next to your script.

Usage

from termcolor import colored

print colored('hello', 'red'), colored('world', 'green')

The tip and the example are from this thread.

Update (20110518)

If you want to print something in red (warning/error) or green (OK), here is a simplified solution:

colorred = "\033[01;31m{0}\033[00m"
colorgrn = "\033[1;36m{0}\033[00m"

print colorred.format("Warning! Reactor meltdown. Evacuate immediately!")
print colorgrn.format("Ha-ha, just kidding!")

Same thing in Java:

String colorred = "\033[01;31m%s\033[00m\n";
System.out.printf(colorred, "# Warning! Approaching light speed. Fasten your seatbelts.");

StringBuilder functionality in Python

Problem

You need to concatenate lots of string elements. Under Java we use a StringBuilder for this, but how to do that in Python?

Solution #1

Use a list, and join the elements of the list at the end. This is much more efficient than concatenating strings since strings are immutable objects, thus if you concatenate a string with another, the result is a NEW string object (the problem is the same with Java strings).

Example:

def g():
    sb = []
    for i in range(30):
        sb.append("abcdefg"[i%7])

    return ''.join(sb)

print g()   # abcdefgabcdefgabcdefgabcdefgab

Solution #2 (update 20120110)

Use a StringIO object and print to it. In short:

from cStringIO import StringIO

out = StringIO()
print >>out, 'arbitrary text'    # 'out' behaves like a file
return out.getvalue()