Better wording for some documentation

doc/extending/optimization.txt

@@ -21,9 +21,10 @@ In this section we will define a couple optimizations on doubles.
 
 .. note::
 
-   There is the optimization tag `cxx_only` that tell this
-   optimization will insert Op that only have c code. So we should not
-   run them when we don't have a c++ compiler.
+   The optimization tag `cxx_only` is used for optimizations that insert
+   Ops which have no Python implementation (so they only have C code).
+   Optimizations with this tag are skipped when there is no C++ compiler
+   available.
 
 Global and local optimizations
 ==============================

doc/library/config.txt

@@ -410,17 +410,18 @@ import theano and print the config variable, as in:
 .. attribute:: config.cxx
 
 
-    Default: 'g++' if g++ is present. '' Otherwise.
+    Default: 'g++' if g++ is present. Empty string otherwise.
 
-    Tell the c++ compiler to use. If empty, don't compile c++ code.
-    We automatically detect if g++ is present and disable it if not
-    present.
+    Indicates which C++ compiler to use. If empty, no C++ code is compiled.
+    Theano automatically detects whether g++ is present and disables
+    C++ compilation when it is not.
 
     We print a warning if we detect that g++ is not present. It is
-    recommended to run with c++ compilation as Theano will be much
+    recommended to run with C++ compilation as Theano will be much
     slower otherwise.
 
-    Currently only g++ is supported, but supporting others is easy.
+    Currently only g++ is supported, but supporting other compilers should
+    not be too difficult.
 
 .. attribute:: optimizer_excluding
 

theano/compile/mode.py

@@ -86,7 +86,7 @@ def register_linker(name, linker):
 # If a string is passed as the optimizer argument in the constructor
 # for Mode, it will be used as the key to retrieve the real optimizer
 # in this dictionary
-exclude=[]
+exclude = []
 if not theano.config.cxx:
     exclude = ['cxx_only']
 OPT_FAST_RUN = gof.Query(include=['fast_run'], exclude=exclude)

theano/configdefaults.py

@@ -131,9 +131,10 @@ else:
     enum = EnumStr("")
 
 AddConfigVar('cxx',
-             "The c++ compiler to use. Currently only g++ is"
-             " supported. But supporting more is easy if someone want this."
-             "If it is empty, we don't compile c++ code.",
+             "The C++ compiler to use. Currently only g++ is"
+             " supported, but supporting additional compilers should not be "
+             "too difficult. "
+             "If it is empty, no C++ code is compiled.",
              enum,
              in_c_key=False)
 del enum