Develop Reference

Best implementation of dual-side dict in Python

I mean a dictionary where of you could get the value by key or the key by value depending on what you need.

You could use bidict package which provides a bidirectional map. The syntax looks as follows (taken from the documentation):
>>> from bidict import bidict
>>> element_by_symbol = bidict(H='hydrogen')
>>> element_by_symbol
bidict({'H': 'hydrogen'})
>>> element_by_symbol['H']
'hydrogen'
>>> element_by_symbol.inv
bidict({'hydrogen': 'H'})
>>> element_by_symbol.inv['hydrogen']
'H'
>>> element_by_symbol.inv.inv is element_by_symbol
True
Or you can implement it yourself, for example using one of the solutions provided here.

extract list or tuple inside string

I am getting input from an external device connected via Ethernet, and it is passing several values of string type e.g. value = '(2,2)\n'. I would like to assign these values to a list or tuple variable e.g. final_value = (2,2).
The code I am using is the following:
import socket
sock = socket.socket()
value =sock.recv(buffersize=2048)
formatted_value = eval(value)
I read that the eval function I am using at this moment to get the list is not a very safe approach, as the external device could pass a dangerous script. So, I would like to know if there is any alternative, similar to the function int(), which can be used to get an integer from a string.

Use ast module literal_eval method for a safer eval
import ast
formatted_value = ast.literal_eval(value)

If you know the input contains a tuple
from ast import literal_eval as make_tuple
make_tuple(value)

Well to give the alternative approach you can do.
s = '(2, 2)\n'
s = s.strip()
if s.startswith('(') and s.endswith(')'):
tup = tuple(int(i) for i in s[1:-1].split(','))
print(tup)
Or if you want a list
s = '(2, 2)\n'
s = s.strip()
if s.startswith('(') and s.endswith(')'):
lst = [int(i) for i in s[1:-1].split(',')]
print(lst)

How to convert this string to Unix time?

How to convert this string to Unix time?
t = '20160224122738'
I can write a function to do this, but wanted to know if there was an already-existing simple method that I could use.

An easy way that comes to mind would be:
>>> import time
>>> import datetime
>>> t = '20160224122738'
>>> time.mktime(datetime.datetime.strptime(t, "%Y%m%d%H%M%S").timetuple())
1456309658.0

Try this,
>>> import datetime
>>> t = '20160224122738'
>>> int(datetime.datetime.strptime(t, '%Y%m%d%H%M%S').strftime("%s"))
1456297058

Why doesn't **kwargs interpolate with python ConfigObj?

I'm using ConfigObj in python with Template-style interpolation. Unwrapping my config dictionary via ** doesn't seem to do interpolation. Is this a feature or a bug? Any nice workarounds?
$ cat my.conf
foo = /test
bar = $foo/directory
>>> import configobj
>>> config = configobj.ConfigObj('my.conf', interpolation='Template')
>>> config['bar']
'/test/directory'
>>> '{bar}'.format(**config)
'$foo/directory'
I'd expect the second line to be /test/directory. Why doesn't interpolation work with **kwargs?

When unpacking the keyword argument, then a new object is created: of type dict. This dictionary contains the the raw-values of the configuration (no interpolation)
Demonstration:
>>> id(config)
31143152
>>> def showKeywordArgs(**kwargs):
... print(kwargs, type(kwargs), id(kwargs))
...
>>> showKeywordArgs(**config)
({'foo': '/test', 'bar': '$foo/directory'}, <type 'dict'>, 35738944)
To resolve your problem you could create an expanded version of your configuration like this:
>>> expandedConfig = {k: config[k] for k in config}
>>> '{bar}'.format(**expandedConfig)
'/test/directory'
Another more elegant way is to simply avoid unpacking: This can be achieved by using the function string.Formatter.vformat:
import string
fmt = string.Formatter()
fmt.vformat("{bar}", None, config)

I have had a similar problem.
A workaround is to use configobj's function ".dict()". This works because configobj returns a real dictionary, which Python knows how to unpack.
Your example becomes:
>>> import configobj
>>> config = configobj.ConfigObj('my.conf', interpolation='Template')
>>> config['bar']
'/test/directory'
>>> '{bar}'.format(**config.dict())
'/test/directory'

Convert an IPv4 range (start and end) to slash notation in Python?

Is there a script available to convert a starting and ending IP address to a slash notation?
Example:
>>> ip_long = '10.182.71.0-10.182.75.255'
>>> convert_to_slash(ip_long)
10.182.71.0/24, 10.182.72.0/22

Use summarize_address_range() from ipaddress, which is part of the Python 3 standard library (and backported to Python 2).
>>> import ipaddress
>>> first = ipaddress.IPv4Address('10.182.71.0')
>>> last = ipaddress.IPv4Address('10.182.75.255')
>>> summary = ipaddress.summarize_address_range(first, last)
>>> list(summary)
[IPv4Network('10.182.71.0/24'), IPv4Network('10.182.72.0/22')]

Google's ipaddr-py library has a method called summarize_address_range(first, last).
summarize_address_range(first, last):
"""Summarize a network range given the first and last IP addresses.
Example:
>>> summarize_address_range(IPv4Address('1.1.1.0'),
IPv4Address('1.1.1.130'))
[IPv4Network('1.1.1.0/25'), IPv4Network('1.1.1.128/31'),
IPv4Network('1.1.1.130/32')]
Args:
first: the first IPv4Address or IPv6Address in the range.
last: the last IPv4Address or IPv6Address in the range.
Returns:
The address range collapsed to a list of IPv4Network's or
IPv6Network's.
Raise:
TypeError:
If the first and last objects are not IP addresses.
If the first and last objects are not the same version.
ValueError:
If the last object is not greater than the first.
If the version is not 4 or 6.
"""

Another solution:
from ipaddress import IPv4Address, summarize_address_range
a=" ".join(map(str, summarize_address_range(IPv4Address('8.8.8.8'), IPv4Address('8.8.9.1'))))
print(a)