Python libraries

Questions about python libraries.

When I write a program, how would I know that I need to use a library?
How and where can I find that library considering that many libraries have weird names that do not indicate what a particular library can be used for.

Hi Sdca,

You will know when you need a certain module if get a NameError at runtime. A NameError occurs when you try to use a variable, function, or module that doesn’t exist or wasn’t used in a valid way.

For example, the following code will give a NameError: name ‘random’ is not defined because the program does not know what random is.

print(random.randint(1,9))

Therefore, you have to import random for this program to work correctly.

import random

print(random.randint(1,9))

Builtin Libraries

If you want to get familiar with and see a list of Python-builtin libraries use the following code:

print(dir(__builtins__))

Output

['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EncodingWarning', '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', 'WindowsError', 'ZeroDivisionError', '__build_class__', '__debug__', '__doc__', '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'aiter', 'all', 'anext', 'any', 'ascii', 'bin', 'bool', 'breakpoint', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', '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', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']

The help() function

Furthermore, if you want more information on each Built-in, you can use the help() function which is like so which is used to get the documentation of specified module, class, function, variables etc.

help(zip)

Output

Help on class zip in module builtins:

class zip(object)
 |  zip(*iterables, strict=False) --> Yield tuples until an input is exhausted.
 |  
 |     >>> list(zip('abcdefg', range(3), range(4)))
 |     [('a', 0, 0), ('b', 1, 1), ('c', 2, 2)]
 |  
 |  The zip object yields n-length tuples, where n is the number of iterables
 |  passed as positional arguments to zip().  The i-th element in every tuple
 |  comes from the i-th iterable argument to zip().  This continues until the
 |  shortest argument is exhausted.
 |  
 |  If strict is true and one of the arguments is exhausted before the others,
 |  raise a ValueError.
 |  
 |  Methods defined here:
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __next__(self, /)
 |      Implement next(self).
 |  
 |  __reduce__(...)
 |      Return state information for pickling.
 |  
 |  __setstate__(...)
 |      Set state information for unpickling.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.

Here is a good reference link that list all built-ins and gives a better description of each built-in. Last but not least, the more you practice the more you will get familiar with what packages you need. I hope this helps!

Best regards,