Question: I want to plot the tree generated by DEAP using pygraphviz. I tried to follow the example in this [DEAP document](https://deap.readthedocs.io/en/master/tutorials/advanced/gp.html), but got the following error:

```
Traceback (most recent call last):
  File "<input>", line 24, in <module>
  File "C:\Users\xxyao\program\anaconda\envs\rf\lib\site-packages\pygraphviz\agraph.py", line 1399, in layout
    data = self._run_prog(prog, ' '.join([args, "-T", fmt]))
  File "C:\Users\xxyao\program\anaconda\envs\rf\lib\site-packages\pygraphviz\agraph.py", line 1364, in _run_prog
    raise IOError(b"".join(errors).decode(self.encoding))
OSError: Format: "dot" not recognized. Use one of:

```

It seems like should be some words after the `Use one of:` but there is not. My environment is `Python==3.6`,`graphviz==3.41`,`pygraphviz==1.5`.The `graphviz`and `pygraphviz` are installed via `conda`.

By the way, I tried the following method: 

1. install graphviz and add `C:\Program Files (x86)\Graphviz2.38\bin` to system environment.
2. `conda install pydot`, `conda install pydot-ng`

but it still doesn't work.

Further infomation: Other layout provided by `pygraphviz` such as `neato fdp twopi` works well. Only the `dot` doesn't work!

Answer: 
I had the same problem. And solved it by executed "dot -c" in conda cmd.
Exactly, just open anaconda Prompt environment
and type "dot -c" command and error fixed.

[enter image description here](https://i.stack.imgur.com/k0EMB.png)