Python snippets #2

Some code snippets taken from: Nifty python tricks.

my_dict = {i: i * i for i in xrange(100)} 
my_set = {i * 15 for i in xrange(100)}

import ast 
expr = "[1, 2, 3]" 
my_list = ast.literal_eval(expr)

# Debugging - set breakpoint in your code:
import pdb
(...)
pdb.set_trace()
 
# Profiling
python -m cProfile script.py

Using list.reverse() reverses the list in-place. If we want a copy leaving the original list (or string) intact:

# Also for strings -
a = [1,2,3,4]
reversed = a[::-1]

from pprint import pprint 
pprint(my_dict)

According to this Reddit thread, the most common / useful Python modules.

• sys, os, math, shutil, tempfile, re, string, glob
• collections
• csv
• datetime
• unittest
• json / ujson
• buildout
• BeautifulSoup
• docopt / argparse / optparse
• decimal
• hashlib
• itertools, functools
• urllib, urllib2, urlparse, requests, httplib, smtplib
• socket
• io (StringIO, BytesIO)
• subprocess
• logging
• operator
• random
• pickle / cpickle
• gzip
• xml.etree.ElementTree
• numpy, scipy, matplotlib, pandas
• scikit-learn
• configparser
• struct, copy
• pprint
• timeit
• mechanize, selenium

From this reddit thread, a way to wrap requests to the requests module:

class RequestError(Exception):
    pass
 
def _try_page(url, attempt_number=1):
    max_attempts = 3
    try:
        response = requests.get(url)
        response.raise_for_status()
    except (requests.exceptions.RequestException, socket_error, S3ResponseError, BotoServerError) as e:
        if attempt_number < max_attempts:
            attempt = attempt_number + 1
            return _try_page(url, attempt_number=attempt)
        else:
            logger.error(e)
            raise RequestError('max retries exceed when trying to get the page at %s' % url)
 
    return response

From this interesting article, how to implement a "Fuzzy Search" (like the ones in Sublime Text or vim's Ctrl+P) with python and regexps. The idea is to convert the requested string (abc) into a regexp (a.*b.*c.*) and then sort the results by the length of the match group:

>>> collection = ['django_migrations.py', 'django_admin_log.py', 'main_generator.py',
                  'migrations.py', 'api_user.doc', 'user_group.doc', 'accounts.txt', ]
 
>>> import re     # regex module from standard library.
 
>>> def fuzzyfinder(user_input, collection):
        suggestions = []
        pattern = '.*'.join(user_input)   # Converts 'djm' to 'd.*j.*m'
        regex = re.compile(pattern)  # Compiles a regex.
        for item in collection:
            match = regex.search(item)   # Checks if the current item matches the regex.
            if match:
                suggestions.append((len(match.group()), match.start(), item))
        return [x for _, _, x in sorted(suggestions)]
 
>>> print fuzzyfinder('mig', collection)
['migrations.py', 'django_migrations.py', 'main_generator.py', 'django_admin_log.py']

conn = pymysql.connect(host='localhost', user='username',
                       passwd='password', db='database',
                       charset='utf8')

And when each cursor is created:

cur.execute('SET NAMES utf8;')
cur.execute('SET CHARACTER SET utf8;')
cur.execute('SET character_set_connection=utf8;')

</code>

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