docs: Resolve several exception handling/propagation issues in the examples.

docs/examples/tutorial/profiling_tutorial/calc_pi_3.pyx

@@ -2,7 +2,7 @@
 
 # calc_pi.pyx
 
-cdef inline double recip_square(int i):
+cdef inline double recip_square(int i) except -1.0:
     return 1. / (i * i)
 
 def approx_pi(int n=10000000):

docs/examples/tutorial/profiling_tutorial/calc_pi_4.pyx

@@ -5,7 +5,7 @@
 cimport cython
 
 @cython.profile(False)
-cdef inline double recip_square(int i):
+cdef inline double recip_square(int i) except -1.0:
     return 1. / (i * i)
 
 def approx_pi(int n=10000000):

docs/examples/tutorial/string/c_func.pyx

@@ -8,7 +8,8 @@ cdef Py_ssize_t n = strlen(hello_world)
 cdef char* c_call_returning_a_c_string():
     cdef char* c_string = <char *> malloc((n + 1) * sizeof(char))
     if not c_string:
-        raise MemoryError()
+        return NULL  # malloc failed
+
     strcpy(c_string, hello_world)
     return c_string
 
@@ -16,7 +17,7 @@ cdef char* c_call_returning_a_c_string():
 cdef void get_a_c_string(char** c_string_ptr, Py_ssize_t *length):
     c_string_ptr[0] = <char *> malloc((n + 1) * sizeof(char))
     if not c_string_ptr[0]:
-        raise MemoryError()
+        return  # malloc failed
 
     strcpy(c_string_ptr[0], hello_world)
     length[0] = n

docs/examples/userguide/early_binding_for_speed/rectangle_cdef.pyx

@@ -9,7 +9,7 @@ cdef class Rectangle:
         self.y1 = y1
 
     cdef int _area(self):
-        area = (self.x1 - self.x0) * (self.y1 - self.y0)
+        cdef int area = (self.x1 - self.x0) * (self.y1 - self.y0)
         if area < 0:
             area = -area
         return area

docs/examples/userguide/language_basics/cdef_block.pyx

@@ -8,5 +8,5 @@ cdef:
     float a
     Spam *p
 
-    void f(Spam *s):
+    void f(Spam *s) except *:
         print(s.tons, "Tons of spam")

docs/examples/userguide/parallelism/breaking_loop.pyx

 from cython.parallel import prange
 
-cdef int func(Py_ssize_t n):
+cdef int func(Py_ssize_t n) except -1:
     cdef Py_ssize_t i
 
     for i in prange(n, nogil=True):

docs/src/tutorial/profiling_tutorial.rst

@@ -200,18 +200,21 @@ profile script then at all. The script now outputs the following:
            1    0.000    0.000    4.406    4.406 <string>:1(<module>)
            1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
 
-We gained 1.8 seconds. Not too shabby. Comparing the output to the previous, we
-see that recip_square function got faster while the approx_pi function has not
-changed a lot. Let's concentrate on the recip_square function a bit more. First
-note, that this function is not to be called from code outside of our module;
-so it would be wise to turn it into a cdef to reduce call overhead. We should
-also get rid of the power operator: it is turned into a pow(i,2) function call by
-Cython, but we could instead just write i*i which could be faster. The
+We gained 1.8 seconds.  Not too shabby.  Comparing the output to the previous, we
+see that the ``recip_square()`` function got faster while the ``approx_pi()``
+function has not changed a lot.  Let's concentrate on the recip_square function
+a bit more.  First, note that this function is not to be called from code outside
+of our module; so it would be wise to turn it into a cdef to reduce call overhead.
+We should also get rid of the power operator: it is turned into a pow(i,2) function
+call by Cython, but we could instead just write i*i which could be faster.  The
 whole function is also a good candidate for inlining.  Let's look at the
 necessary changes for these ideas:
 
 .. literalinclude:: ../../examples/tutorial/profiling_tutorial/calc_pi_3.pyx
 
+Note that the ``except`` declaration is needed in the signature of ``recip_square()``
+in order to propagate division by zero errors.
+
 Now running the profile script yields:
 
 .. code-block:: none

docs/src/tutorial/strings.rst

@@ -124,6 +124,9 @@ Python variable::
     from c_func cimport c_call_returning_a_c_string
 
     cdef char* c_string = c_call_returning_a_c_string()
+    if c_string is NULL:
+        ...  # handle error
+
     cdef bytes py_string = c_string
 
 A type cast to :obj:`object` or :obj:`bytes` will do the same thing::