Useful python snippets

useful_python_snippets.py

#############################################################################
# Generate Dict from a List of Dict
ticker = [
 {
   'symbol': 'ABC',
   'price': 100.0
 }, 
 {
   'symbol': 'CDE',
   'price': 105.0
 }
]
prices = {t['symbol']: t for t in ticker}
# prices: 
# {
#   'ABC': {
#     'symbol': 'ABC',
#     'price': 100.0
#   }, 
#   'CDE': {
...
# }

#############################################################################
# Subclass UserDict to create object with dict 
# - able to acccess property by key, for example obj1['prop1']
# - able to access property by obj 'dot' reference, for example obj1.prop1 

from collections import UserDict # using python 3

class MyUserDict(UserDict):
  def __init__(self, data={}, **kw):
    UserDict.__init__(self)
    self.update(data)
    self.update(kw)    
    
  def __getattr__(self, attr):
    return self.get(attr)
  
  def __setattr__(self, key, value):
    self.__dict__.update({key: value})
    
  def test():
    sample_data = {'b': 2, 'a': 1}
    t = MyUserDict(sample_data, c=1)
    assert t['a'] == 1 
    assert t.a == 1
    
    t.b=10
    assert t.b == 10
    
    print("ALL tests passed!")
    

MyUserDict.test()


##############################################
# Array of hashmap to String and vice versa #

import json 

t = [
  {'a': 1, 'b': '2'}
]

s = json.dumps(t)
print(s)

t = json.loads(s)
print(t)


##############################################
# LOGGING TO FILE AND CONSOLE #

import logging
import sys
import datetime
from logging.handlers import RotatingFileHandler

fmt = logging.Formatter("%(asctime)s [%(levelname)-5.5s] L%(lineno)s: %(message)s", datefmt = '%Y/%m/%d %I:%M:%S %p')
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)


fileHandler = RotatingFileHandler(
  f"{sys.argv[0]}.log", maxBytes=(1024*1024*10), backupCount=7)
fileHandler.setFormatter(fmt)
logger.addHandler(fileHandler)

consoleHandler = logging.StreamHandler()
consoleHandler.setFormatter(fmt)
logger.addHandler(consoleHandler)

logger.info(datetime.datetime.now())



##############################################
# Compare 2 dicts except some keys
def compare_dict(d1, d2, ignore):
  for k in d1:
    if k in ignore:
      continue
    try:
      if d1[k] != d2[k]:
        return False
    except KeyError:
      return False
  return True

d1 = {'price': 1000.0, 'position': 'long', 'action': 'hold', 'warning': ''}
d2 = {'price': 1001.0, 'position': '', 'action': 'hold', 'warning': ''}
d3 = {'price': 1002.0, 'position': 'long', 'action': 'hold', 'warning': ''}

print(compare_dict(d1, d2, ['price']))
print(compare_dict(d2, d3, ['price']))
print(compare_dict(d1, d3, ['price']))



##############################################
# Convert a dictionary containing unicode string, non string into a json loadable object
def convert_dict_to_json(data, convert_unicode_to_string=True):
    if isinstance(data, basestring):
        return str(data)
    elif isinstance(data, unicode):
        if convert_unicode_to_string:
            return data.encode('utf-8')
        else:
            return data
    elif isinstance(data, collections.Mapping):
        return dict(map(convert_dict_to_json, data.iteritems()))
    elif isinstance(data, collections.Iterable):
        return type(data)(map(convert_dict_to_json, data))
    else:
        return str(data)

##############################################
# Check if a key is in a dict
if myKey in dict:
    do_some_work
else:
    pass
# Option 2 - try exception
try:
    do_some_work(dict[myKey])
except KeyError:
    pass

##############################################
# String format
>>> "{:0>2}".format("1")  # Works for both numbers and strings.
'01'
>>> "{:02}".format(1)  # Only works for numbers.
'01'


##############################################
# Connect to HSQLDB 

import jaydebeapi

conn = jaydebeapi.connect("org.hsqldb.jdbcDriver", 
                          "jdbc:hsqldb:hsql://localhost:9000/db", 
                          ["SA", ""], 
                          "/home/user_id/hsqldb-2.4.0/hsqldb/lib/hsqldb.jar",)
curs = conn.cursor()
query = """
SELECT * 
FROM test
WHERE id = ?
"""
curs.execute(query, (some_id))
print curs.fetchall()
curs.close()
conn.close()