Can't pretty-print dicts or sets containing non-Expr objects

[rlamy]

In isympy:

In [1]: {Basic(): 1, Basic(Basic()): 2}
<long traceback>
AttributeError: 'Basic' object has no attribute 'as_base_exp'

The problem is that Basic._compare_pretty() assumes that its arguments are instances of Expr.

Original issue for #5306: http://code.google.com/p/sympy/issues/detail?id=2207
Original author: https://code.google.com/u/101272611947379421629/
Original owner: https://code.google.com/u/101272611947379421629/

[rlamy]

There's the same problem with sets. Basic._compare_pretty() is essentially broken and should be replaced with the new sort-key mechanism everywhere (cf. issue 4590 ).

I'm upping he priority on this because it's a serious usability problem for objects deriving from Basic but not from Expr.

**Summary:** Can't pretty-print dicts or sets containing non-Expr objects  
**Labels:** -Priority-Medium Priority-High Milestone-Release0.7.1  
**Blockedon:** 4590  

Referenced issues: #4590
Original comment: http://code.google.com/p/sympy/issues/detail?id=2207#c1
Original author: https://code.google.com/u/101272611947379421629/

[rlamy]

It's actually easy to fix. There's a single line to change and a few tests to update.
I've added the commit to PR #326 ( https://github.com/sympy/sympy/pull/326 ).

**Status:** Started  
**Labels:** NeedsReview  
**Blockedon:** -1491  

Original comment: http://code.google.com/p/sympy/issues/detail?id=2207#c2
Original author: https://code.google.com/u/101272611947379421629/

[asmeurer]

This was pushed.

**Status:** Fixed  
**Labels:** -NeedsReview PassedReview  

Original comment: http://code.google.com/p/sympy/issues/detail?id=2207#c3
Original author: https://code.google.com/u/asmeurer@gmail.com/