You might look at the preorder_traversal() and postorder_traversal() functions
in sympy/utilities/iterables.py:
In [4]: a = (x + 2)*(x + 1)**2
In [5]: from sympy.utilities.iterables import preorder_traversal,
postorder_traversal
In [6]: preorder_traversal(a)
Out[6]: <generator object preorder_traversal at 0x102b099b0>
In [7]: list(preorder_traversal(a))
Out[7]:
⎡ 2 2 ⎤
⎣(1 + x) ⋅(2 + x), (1 + x) , 1 + x, 1, x, 2, 2 + x, 2, x⎦
In [8]: list(postorder_traversal(a))
Out[8]:
⎡ 2 2 ⎤
⎣1, x, 1 + x, 2, (1 + x) , 2, x, 2 + x, (1 + x) ⋅(2 + x)⎦
Also, if you are only interested in visualizing, the print_tree() function can
help:
In [9]: print_tree(a)
Mul: (1 + x)**2*(2 + x)
+-Pow: (1 + x)**2
| +-Add: 1 + x
| | +-One: 1
| | | prime: True
| | | real: True
| | | comparable: True
| | | finite: True
| | | commutative: True
| | | infinitesimal: False
| | | nonpositive: False
| | | composite: False
| | | positive: True
| | | noninteger: False
| | | negative: False
| | | nonnegative: True
| | | zero: False
| | | complex: True
| | | bounded: True
| | | rational: True
| | | unbounded: False
| | | integer: True
| | | imaginary: False
| | | nonzero: True
| | | irrational: False
| | +-Symbol: x
| | comparable: False
| +-Integer: 2
| real: True
| nonzero: True
| comparable: True
| commutative: True
| nonpositive: False
| unbounded: False
| noninteger: False
| complex: True
| nonnegative: True
| zero: False
| infinitesimal: False
| bounded: True
| negative: False
| rational: True
| positive: True
| integer: True
| imaginary: False
| finite: True
| irrational: False
+-Add: 2 + x
+-Integer: 2
| real: True
| nonzero: True
| comparable: True
| commutative: True
| nonpositive: False
| unbounded: False
| noninteger: False
| complex: True
| nonnegative: True
| zero: False
| infinitesimal: False
| bounded: True
| negative: False
| rational: True
| positive: True
| integer: True
| imaginary: False
| finite: True
| irrational: False
+-Symbol: x
comparable: False
If you don't want to see all the assumptions stuff, you will have to edit the
code in sympy/printing/tree.py.
Aaron Meurer
On Jun 22, 2010, at 1:36 AM, nelson wrote:
> Thank you, it worked well. I can't find how in sympy i can obtain the
> entire expression parsing tree. I want to be able to navigate from my
> app, selecting part of the expression (having the expression tree and
> navigation functions, this would be very easy), and applying to this
> expression some operation.
>
> Is there some common approach to this problem?
>
> thanks
>
> On Jun 15, 11:15 pm, "Aaron S. Meurer" <asmeu...@gmail.com> wrote:
>> Hi.
>>
>> The easiest way to do this is to use .args:
>>
>> In [1]: a = (x + 2)*(x + 1)**2
>>
>> In [2]: a
>> Out[2]:
>> 2
>> (1 + x) ⋅(2 + x)
>>
>> In [3]: a.args
>> Out[3]:
>> ⎛ 2 ⎞
>> ⎝(1 + x) , 2 + x⎠
>>
>> In [4]: a.args[0]
>> Out[4]:
>> 2
>> (1 + x)
>>
>> In [5]: a.args[0].expand()*a.args[1]
>> Out[5]:
>> ⎛ 2⎞
>> (2 + x)⋅⎝1 + 2⋅x + x ⎠
>>
>> Aaron Meurer
>> On Jun 15, 2010, at 12:31 PM, nelson wrote:
>>
>>
>>
>>
>>
>>
>>
>>> hi all!
>>> i am evaluating sympy for a project i'm doing. Basically i want to
>>> be able to extract a part of an expression, for examplre (x+1)^2 out
>>> of (x+2)*(x+1)^2 and performing an operation on it. For example,,
>>> expanding the (x+1)^2 term wold return the expression
>>> (x+2)*(x^2+2*x+1)
>>
>>> is it possibile using sympy? how can i accomplish this task?
>>
>>> thanks in advance,
>>> Andrea
>>
>>> --
>>> You received this message because you are subscribed to the Google Groups
>>> "sympy" group.
>>> To post to this group, send email to sy...@googlegroups.com.
>>> To unsubscribe from this group, send email to
>>> sympy+unsubscr...@googlegroups.com.
>>> For more options, visit this group
>>> athttp://groups.google.com/group/sympy?hl=en.
>
> --
> You received this message because you are subscribed to the Google Groups
> "sympy" group.
> To post to this group, send email to sy...@googlegroups.com.
> To unsubscribe from this group, send email to
> sympy+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/sympy?hl=en.
>
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To post to this group, send email to sy...@googlegroups.com.
To unsubscribe from this group, send email to
sympy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sympy?hl=en.
