Unlock Python’s Hidden Tricks: Comprehensions, Counters, and Quick RPC

1. Dictionary and Set Comprehensions

Most Python programmers know list comprehensions. A list comprehension provides a concise way to create a list.

>> some_list = [1, 2, 3, 4, 5]
>>> another_list = [x + 1 for x in some_list]
>>> another_list
[2, 3, 4, 5, 6]

Since Python 3.1 (and even 2.7) the same syntax can create sets and dictionaries.

# Set Comprehensions
>>> some_list = [1,2,3,4,5,2,5,1,4,8]
>>> even_set = {x for x in some_list if x % 2 == 0}
>>> even_set
{8, 2, 4}
# Dict Comprehensions
>>> d = {x: x % 2 == 0 for x in range(1, 11)}
>>> d
{1: False, 2: True, 3: False, 4: True, 5: False, 6: True, 7: False, 8: True, 9: False, 10: True}

Set literals can also be written directly:

>> my_set = {1, 2, 1, 2, 3, 4}
>>> my_set
{1, 2, 3, 4}

2. Counting with Counter

The collections module provides a Counter class for easy counting.

>> from collections import Counter
>>> c = Counter('hello world')
>>> c
Counter({'l': 3, 'o': 2, ' ': 1, 'e': 1, 'd': 1, 'h': 1, 'r': 1, 'w': 1})
>>> c.most_common(2)
[('l', 3), ('o', 2)]

3. Pretty‑Printing JSON

Using the json module with the indent parameter produces readable output.

>> import json
>>> print(json.dumps(data))          # No indentation
>>> print(json.dumps(data, indent=2))  # With indentation

4. Quick One‑off Web Service with XML‑RPC

A minimal file‑reading service can be built with SimpleXMLRPCServer.

from SimpleXMLRPCServer import SimpleXMLRPCServer

def file_reader(file_name):
    with open(file_name, 'r') as f:
        return f.read()

server = SimpleXMLRPCServer(('localhost', 8000))
server.register_introspection_functions()
server.register_function(file_reader)
server.serve_forever()

Client side:

import xmlrpclib
proxy = xmlrpclib.ServerProxy('http://localhost:8000/')
proxy.file_reader('/tmp/secret.txt')

5. The Vibrant Python Open‑Source Community

All examples use only the Python standard library; many third‑party libraries are also available for a wide range of tasks.