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What are the built-in functions?

January 19, 2018 Leave a comment

Problem
How to figure out the built-in functions in Python? Of course, you can look up the documentation, but now the exercise is to list them in the Python shell.

Solution

In [1]: import builtins

In [2]: dir(builtins)
Out[2]: 
['ArithmeticError',
 'AssertionError',
 'AttributeError',
 'BaseException',
 'BlockingIOError',
 'BrokenPipeError',
 'BufferError',
 'BytesWarning',
 'ChildProcessError',
 'ConnectionAbortedError',
 'ConnectionError',
 'ConnectionRefusedError',
 'ConnectionResetError',
 'DeprecationWarning',
 'EOFError',
 'Ellipsis',
 'EnvironmentError',
 'Exception',
 'False',
 'FileExistsError',
 'FileNotFoundError',
 'FloatingPointError',
 'FutureWarning',
 'GeneratorExit',
 'IOError',
 'ImportError',
 'ImportWarning',
 'IndentationError',
 'IndexError',
 'InterruptedError',
 'IsADirectoryError',
 'KeyError',
 'KeyboardInterrupt',
 'LookupError',
 'MemoryError',
 'ModuleNotFoundError',
 'NameError',
 'None',
 'NotADirectoryError',
 'NotImplemented',
 'NotImplementedError',
 'OSError',
 'OverflowError',
 'PendingDeprecationWarning',
 'PermissionError',
 'ProcessLookupError',
 'RecursionError',
 'ReferenceError',
 'ResourceWarning',
 'RuntimeError',
 'RuntimeWarning',
 'StopAsyncIteration',
 'StopIteration',
 'SyntaxError',
 'SyntaxWarning',
 'SystemError',
 'SystemExit',
 'TabError',
 'TimeoutError',
 'True',
 'TypeError',
 'UnboundLocalError',
 'UnicodeDecodeError',
 'UnicodeEncodeError',
 'UnicodeError',
 'UnicodeTranslateError',
 'UnicodeWarning',
 'UserWarning',
 'ValueError',
 'Warning',
 'ZeroDivisionError',
 '__IPYTHON__',
 '__build_class__',
 '__debug__',
 '__doc__',
 '__import__',
 '__loader__',
 '__name__',
 '__package__',
 '__spec__',
 'abs',
 'all',
 'any',
 'ascii',
 'bin',
 'bool',
 'bytearray',
 'bytes',
 'callable',
 'chr',
 'classmethod',
 'compile',
 'complex',
 'copyright',
 'credits',
 'delattr',
 'dict',
 'dir',
 'display',
 'divmod',
 'enumerate',
 'eval',
 'exec',
 'filter',
 'float',
 'format',
 'frozenset',
 'get_ipython',
 'getattr',
 'globals',
 'hasattr',
 'hash',
 'help',
 'hex',
 'id',
 'input',
 'int',
 'isinstance',
 'issubclass',
 'iter',
 'len',
 'license',
 'list',
 'locals',
 'map',
 'max',
 'memoryview',
 'min',
 'next',
 'object',
 'oct',
 'open',
 'ord',
 'pow',
 'print',
 'property',
 'range',
 'repr',
 'reversed',
 'round',
 'set',
 'setattr',
 'slice',
 'sorted',
 'staticmethod',
 'str',
 'sum',
 'super',
 'tuple',
 'type',
 'vars',
 'zip']
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Categories: python Tags:

BASE64 as URL parameter

January 1, 2018 Leave a comment

Problem
In a REST API, I wanted to pass a URL as a BASE64-encoded string, e.g. “http://host/api/v2/url/aHR0cHM6...“. It worked well for a while but I got an error for a URL. As it turned out, a BASE64 string can contain the “/” sign, and it caused the problem.

Solution
Replace the “+” and “/” signs with “-” and “_“, respectively. Fortunately, Python has functions for that (see here).

Here are my modified, URL-safe functions:

def base64_to_str(b64):
    return base64.urlsafe_b64decode(b64.encode()).decode()

def str_to_base64(s):
    data = base64.urlsafe_b64encode(s.encode())
    return data.decode()

You can also quote and unquote a URL instead of using BASE64:

>>> url = "https://www.youtube.com/watch?v=V6w24Lg3zTI"
>>>
>>> import urllib.parse
>>>
>>> new = urllib.parse.quote(url)
>>>
>>> new
>>> 'https%3A//www.youtube.com/watch%3Fv%3DV6w24Lg3zTI'    # notice the "/" signs!
>>>
>>> urllib.parse.quote(url, safe='')
>>> 'https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DV6w24Lg3zTI'    # no "/" signs!
>>>
>>> new = urllib.parse.quote(url, safe='')
>>>
>>> urllib.parse.unquote(new)
>>> 'https://www.youtube.com/watch?v=V6w24Lg3zTI'
Categories: python Tags: , , ,