Python Tips

Python Tips#

The help function#

You can get context-sensitive help to functions, methods and classes with help() function.

import time
print(help(time.asctime))

Help on built-in function asctime in module time:

asctime(...)
    asctime([tuple]) -> string
    
    Convert a time tuple to a string, e.g. 'Sat Jun 06 16:26:11 1998'.
    When the time tuple is not present, current time as returned by localtime()
    is used.

None

help() utilizes the triple-quoted comments called docstrings, so that documentation you write for your own functions is also available through help():

Everything is an object#

One consequence of the dynamic typing is that Python can treat everything it manages technically in the same way. Everything is an object is a common phrase describing how Python works. There is no fundamental difference between a function and an integer. Many advanced features of Python are built on this concept.

Using the Python documentation#

Even advanced programmers can not remember every little python function and usage by head. But a good programmer knows where to find the crucial information.

Of course the Python Documentation are a good resource a faster way towards crucial documentation exist.

It is pydoc. Pydoc usuage docstrings and since every good piece of python software makes use of docstrings using pdoc is the shortest path towards helpful information.

The way to start pydoc for browsing documentation is:

pydoc -p [portnumber]

The pydoc module automatically generates documentation from Python modules.

Pydoc command can be used within a notebook. But the most used way to display help of a function or module is typing:

help(function)

This invokes pydoc and displays the docstring (if used) on how a function should be used.

Introspection#

Introspection is a feature of Python by which you can examine objects (including variables, functions, classes, modules) inside a running Python environment (a program or shell session).

Exploring the namespace#

In Python all objects (variables, modules, classes, functions and your main program) are boxes called namespaces. You can imagine the namespace of an object as the data and functions inside than object. You can explore a namespace with the dir() function.

Exploring the namespace of a variable#

With a string object, you see all the string methods:

s = "Emily"
print(dir(s))

Gives output:

['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Exploring the namespace of a module:#

The same works for a module you import:

    import time
    print(dir(time))