- By Vasudev Ram - Online Python training / SQL training / Linux training
Tree image attribution
Hi, readers,
I was using the pprint module to pretty-print some Python data structures in a program I was writing. Then saw that it has a function called isrecursive.
The docstring for pprint.isrecursive says:
>>> print pprint.isrecursive.__doc__ Determine if object requires a recursive representation.Here is a Python 3 shell session that shows what the isrecursive function does, with a list:
>>> import pprint >>> print(pprint.pprint.__doc__) Pretty-print a Python object to a stream [default is sys.stdout]. >>> a = [] >>> a [] >>> pprint.isrecursive(a) False >>> >>> a.append(a) >>> a [[...]] >>> >>> pprint.isrecursive(a) TrueHow about for a dict?
>>> b = {}
>>> pprint.isrecursive(b)
False
>>>
>>> b[1] = b
>>> b
{1: {...}}
>>> id(b) == id(b[1])
True
>>> pprint.isrecursive(b)
True
How about if an object is recursive, but not directly, like in the above two examples? Instead, it is recursive via a chain of objects:>>> c = [] >>> d = [] >>> e = [] >>> c.append(d) >>> d.append(e) >>> c [[[]]] >>> pprint.isrecursive(c) False >>> e.append(c) >>> c [[[[...]]]] >>> pprint.isrecursive(c) TrueSo we can see that isrecursive is useful to detect some recursive Python object structures.
Interestingly, if I compare c with c[0] (after making c a recursive structure), I get:
>>> c == c[0] Traceback (most recent call last): File "In Python 2, I get:", line 1, in RecursionError: maximum recursion depth exceeded in comparison >>>
RuntimeError: maximum recursion depth exceeded in cmp
Also, relevant XKCD-clone.
The image at the top of the post is of a tree created in the LOGO programming language using recursion.
- Enjoy.
- Vasudev Ram - Online Python training and consulting
I conduct online courses on Python programming, Unix / Linux commands and shell scripting and SQL programming and database design, with course material and personal coaching sessions.
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