Updated Cython wrap_arrays to be an excercise

Author: tleonhardt

cython/wrap_arrays/Readme.md

@@ -24,3 +24,31 @@ Run pytest unit tests to verify everything is working as intended for the Cython
         * setup.py
     * pytest unit tests
         * test_cython_wrapper.py
+        
+        
+## Excercise
+You need to fill in the **TODO:** blocks in **cfastlz.pxd** and **cyfastlz.pyx**
+
+Some useful things to keep in mind:
+
+1. Read the documentation in fastlz.h to understand how the compress() and decompress() functions work.
+2. You can cast from a Python type to a C type using syntax like the following:
+
+```python
+<const uint8_t*>in_buf
+```
+3. In Python, you can use *slicing* to return a subarray, substring, etc using syntax similar to:
+
+```python
+my_array = range(10)
+my_array[2:7]
+[2, 3, 4, 5, 6]
+```
+
+The slice includes the starting index, but excludes the ending index.
+
+You know you are done when the unit test passes.
+
+
+### Solution
+The solution is on the **solutions** branch.  Don't peak until you have given this an honest effort.

cython/wrap_arrays/cfastlz.pxd

@@ -6,5 +6,5 @@ from libc.stdint cimport uint8_t
 
 
 cdef extern from "fastlz.h":
-    int fastlz_compress(const uint8_t* inBuf, int length, uint8_t* output)
-    int fastlz_decompress(const uint8_t* inBuf, int length, uint8_t* output, int maxout)
+    # TODO: Copy function prototypes you want to wrap from the C header file here (without ending semicolon)
+

cython/wrap_arrays/cyfastlz.pyx

@@ -20,14 +20,11 @@ cpdef bytes compress(bytes in_buf):
     # Create the output buffer
     output = bytearray(M)
 
-    # wrap byte arrays to c arrays for the call
-    fcret = cfastlz.fastlz_compress(<const uint8_t*>in_buf, N, <uint8_t*> output)
+    # TODO: Call cfastlz.fastlz_compress().  Make sure to get the return value and to cast Python array type to C type.
 
-    if fcret <=0:
-        return None
+    # TODO: Check for invalid return value and return None if that occurs
 
-    # Return the compressed data as a bytes object
-    return bytes(output[:fcret])
+    # TODO: Return the compressed data as a bytes object
 
 
 cpdef bytes decompress(bytes in_buf):
@@ -43,12 +40,8 @@ cpdef bytes decompress(bytes in_buf):
     M = max(int(4*N), 66)
     output = bytearray(M)
 
-    # wrap byte arrays to c arrays for the call
-    fcret = cfastlz.fastlz_decompress(<const uint8_t*> in_buf, N, <uint8_t*> output, M)
+    # TODO: Call cfastlz.fastlz_decompress().  Make sure to get the return value and to cast Python array type to C type.
 
-    # If error occurs, e.g. the compressed data is corrupted or the output buffer is not large enough, then 0 (zero)
-    if fcret <=0:
-        return None
+    # TODO: Check for invalid return value and return None if that occurs
 
-    # Return the uncompressed data as a bytes object
-    return bytes(output[:fcret])
+    # TODO: Return the uncompressed data as a bytes object