flow.Cache accepts an argument recompute. Instead of commenting out C…

…ache, one can define its behaviour from command line arguments or other runtime settings.

lena/flow/cache.py

@@ -47,10 +47,16 @@ class Cache(object):
         Never unpickle data from an untrusted source.
     """
 
-    def __init__(self, filename, method="cPickle", protocol=2):
+    def __init__(self, filename, recompute=False,
+                 method="cPickle", protocol=2):
         """*filename* is the name of file where to store the cache.
         You can give it *.pkl* extension.
 
+        If *recompute* is ``True``,
+        an existing cache will always be overwritten.
+        This option is typically used if one wants to define
+        cache behaviour from the command line.
+
         *method* can be *pickle* or *cPickle* (faster pickle).
         For Python 3 they are same.
 
@@ -77,11 +83,18 @@ def __init__(self, filename, method="cPickle", protocol=2):
 
         self._filename = filename
         self.protocol = protocol
+        self._recompute = recompute
         # used by meta elements
         self.is_cache = True
 
     def cache_exists(self):
-        """Return ``True`` if file with cache exists and is readable."""
+        """Return ``True`` if file with cache exists and is readable.
+
+        If *recompute* was ``True`` during the initialization,
+        pretend that cache does not exist (return ``False``).
+        """
+        if self._recompute:
+            return False
         return os.access(self._filename, os.R_OK)
 
     def drop_cache(self):
@@ -138,7 +151,8 @@ def alter_sequence(seq):
                         break
             if last_cache_filled_ind is not None:
                 return lena.core.Source(
-                    lena.core.SourceEl(seq[last_cache_filled_ind], call="_load_flow"),
+                    lena.core.SourceEl(seq[last_cache_filled_ind],
+                                       call="_load_flow"),
                     *seq[last_cache_filled_ind+1:]
                 )
         else:

tests/flow/test_cache.py

@@ -5,20 +5,29 @@
 from lena.core import Sequence, Source, LenaTypeError, LenaValueError
 from tests.example_sequences import (
     ASCIILowercase, ASCIIUppercase, ascii_lowercase, ascii_uppercase,
-    lowercase_cached_filename, lowercase_cached_seq, id_
+    lowercase_cached_filename, lowercase_cached_seq, id_,
 )
 from lena.flow.cache import Cache
 from lena.flow.iterators import Slice
 from tests.shortcuts import cnt1, cnt1c
 
 
-def test_cache():
-    s = Source(ascii_lowercase, lowercase_cached_seq)
-    assert "".join(s()) == "abcdefghijklmnopqrstuvwxyz"
-    # cache is actually used
-    s = Source(ascii_uppercase, lowercase_cached_seq)
-    assert "".join(s()) == "abcdefghijklmnopqrstuvwxyz"
-    lowercase_cached_seq[0].drop_cache()
+def test_cache(tmpdir):
+    low_letters = "abcdefghijklmnopqrstuvwxyz"
+    os.chdir(tmpdir)
+
+    # empty cache makes no problems
+    s1 = Source(ascii_lowercase, lowercase_cached_seq)
+    assert "".join(s1()) == low_letters
+
+    # filled cache is actually used
+    s2 = Source(ascii_uppercase, lowercase_cached_seq)
+    assert "".join(s2()) == low_letters
+
+    # recompute works
+    c3 = Cache(lowercase_cached_filename, recompute=True)
+    s3 = Source(ascii_uppercase, c3)
+    assert "".join(s3()) == "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 
 
 # it's a shame, but I had two tests in different files
@@ -64,13 +73,10 @@ def test_cache_2(tmp_path):
     assert res4 == [(1, {'1': 1}), (2, {'2': 2})]
 
 
-def test_alter_sequence():
+def test_alter_sequence(tmpdir):
+    os.chdir(tmpdir)
     cached_to_source = Cache.alter_sequence
-    # remove cache
-    try:
-        os.remove(lowercase_cached_filename)
-    except Exception:
-        pass
+
     lowercase_cache_el = Cache(lowercase_cached_filename)
     el = lowercase_cache_el 
     s0 = Sequence(el)
@@ -93,5 +99,3 @@ def test_alter_sequence():
     # this fails for nested Sequences. To be done.
     assert cached_to_source(s) != s
     assert isinstance(cached_to_source(s), Source)
-
-    lowercase_cache_el.drop_cache()