- 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__Here is a Python 3 shell session that shows what the isrecursive function does, with a list:
Determine if object requires a recursive representation.
>>> import pprintHow about for a dict?
>>> 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)
True
>>> 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 = []So we can see that isrecursive is useful to detect some recursive Python object structures.
>>> d = []
>>> e = []
>>> c.append(d)
>>> d.append(e)
>>> c
[[[]]]
>>> pprint.isrecursive(c)
False
>>> e.append(c)
>>> c
[[[[...]]]]
>>> pprint.isrecursive(c)
True
Interestingly, if I compare c with c[0] (after making c a recursive structure), I get:
>>> c == c[0]In Python 2, I get:
Traceback (most recent call last):
File "", 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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