Adding UnevaluatedExpr() Tutorial

[mohit3011]

This Pull Request Fixes #12230

[mohit3011]

@Upabjojr , please review the changes . Thanks

[Upabjojr]

I would put the code here:
https://github.com/sympy/sympy/blob/master/doc/src/tutorial/manipulation.rst

(Advanced expression manipulation).

[Upabjojr]

Also link the class here: https://github.com/sympy/sympy/blob/master/doc/src/modules/core.rst#expr-1

[mohit3011]

@Upabjojr , I have changed it according to you, please review it . Thanks

[Upabjojr]

Strange... Travis did not start.

[Upabjojr]

The tutorial should not be about the class UnevaluatedExpr, rather about generic methods to keep expressions unevaluated. I think we should also mention evaluate=False.

[Upabjojr]

Added some fixes. Tests are probably still failing.

[mohit3011]

@Upabjojr , do you know why the tests are failing ?

[Upabjojr]

do you know why the tests are failing ?

Your example outputs are wrong.

[mohit3011]

I checked it on terminal in sympy , it can't be wrong

[Yathartha22]

• line 520 the result should be 2*x since the expr variable has not been updated it still has a value of x + x.
• line 526 the result should be (5/7)*(3/4)
• line 531 the result should be x*1/x
• line 539 should be 2*x
  I guess these are the issues in the doc.

[Upabjojr]

I checked it on terminal in sympy , it can't be wrong

Maybe you use a different printer.

[mohit3011]

I have updated the examples

[mohit3011]

@Upabjojr , I checked all the examples once again . There doesn't seem any error in those . I would like to point to core.rst , because I am not really sure about that.
One more thing Since the examples are on continuous basis , so are we assumming that once we import certain class from sympy then we can use it in all example or we have to import it every time.

[Upabjojr]

https://travis-ci.org/sympy/sympy/jobs/206607119

There is still a minor problem. If tests fail, just click on the X near the commit hashtag to see why.

once we import certain class from sympy then we can use it in all example or we have to import it every time.

The doctests are generally sequential while executing the code, so different blocks are treated sequentially in every test. I think it's on a class-level or RST module-level (that is, higher scope is not sequential anymore), but I'm not so sure.

[mohit3011]

@Upabjojr , I don't know why but the travis test is not opening up . This problem has been persistent since last night.

[Upabjojr]

I don't know why but the travis test is not opening up . This problem has been persistent since last night.

Yeah, I think there's some problems with Travis today. I was able to access it one hour ago.

Otherwise, run the tests locally.

[mohit3011]

@Upabjojr , now I think its fine. One runtime error is due to some other module, I guess.

[Upabjojr]

Warning, treated as error:
/home/travis/build/sympy/sympy/doc/src/tutorial/manipulation.rst:471: WARNING: Title underline too short.

That's our file. We need a shorter title.

[mohit3011]

@Upabjojr , finally :)

[mohit3011]

@Upabjojr , how can I run doc tests locally , because I can only see an error related to job time limit exceeded on Travis . Thanks

[Upabjojr]

how can I run doc tests locally , because I can only see an error related to job time limit exceeded on Travis . Thanks

I think that this time Travis had a spurious failure. Restarted.

There is a directory bin in SymPy with scripts to run the tests.

[mohit3011]

@Upabjojr , I have run tests for other modules from bin by using the command like python bin/test "module_name" for testing "module_name".py but for running doc test what should I write ?

[Upabjojr]

I have run tests for other modules from bin by using the command like python bin/test "module_name" for testing "module_name".py but for running doc test what should I write ?

One of those scripts calls the command, just look at the code.