Small but practical functions

small_funcs.py

# parse iso time
datetime.strptime('2019-04-17T09:02:16.00428Z', '%Y-%m-%dT%H:%M:%S.%fZ')


import itertools

def grouper(iterable, n):
    it = iter(iterable)
    while True:
       chunk = tuple(itertools.islice(it, n))
       if not chunk:
           return
       yield chunk
      
# list(grouper(range(102),5))
[(0, 1, 2, 3, 4),
 (5, 6, 7, 8, 9),
 (10, 11, 12, 13, 14),
 (15, 16, 17, 18, 19),
 ...
 (90, 91, 92, 93, 94),
 (95, 96, 97, 98, 99),
 (100, 101)]



def binary_search(data, item):
    left, right = 0, len(data) - 1
    
    while left <= right:
        middle = (left + right) // 2
        
        if item < data[middle]:
            right = middle - 1
        elif item > data[middle]:
            left = middle + 1
        else:
            return middle
        
    return -1

https://en.wikipedia.org/wiki/Autovivification
    
>>> class Tree(dict):
...     def __missing__(self, key):
...         value = self[key] = type(self)()
...         return value

>>> # common names by class, order, genus, and type-species
>>> common_names = Tree()
>>> common_names['Mammalia']['Primates']['Homo']['H. sapiens'] = 'human being'
>>> common_names
{'Mammalia': {'Primates': {'Homo': {'H. sapiens': 'human being'}}}}

>>> # Famous quotes by play, act, scene, and page
>>> quotes = Tree()
>>> quotes['Hamlet'][1][3][3] = 'This above all: to thine own self be true.'
>>> quotes
{'Hamlet': {1: {3: {3: 'This above all: to thine own self be true.'}}}}


def try_parse_datetime(text):
        formats = [
            '%Y-%m-%dT%H:%M:%S.%fZ',
            '%Y-%m-%dT%H:%M:%S.%f',
            '%Y-%m-%dT%H:%M:%S',
        ]
        for f in formats:
            try:
                v = datetime.strptime(text, f)
                return v
            except ValueError:
                pass
        print(text)
        return None


-----  filter byte zeros in S3 objects (for Messytables) ----

obj = bucket.Object(csv_path)

file_content = obj.get()["Body"]

# the code bellow filters out '\0' (byte 0x00) in the csv file
buffer = BytesIO()
for c in file_content.read():
    if c != 0:
        buffer.write(c.to_bytes(1, 'little'))

table_set = CSVTableSet(buffer) # send to Messytables