Import psutil conditionally; install it only in Linux platforms

setup.py

@@ -51,7 +51,10 @@ def main():
 
         python_requires='>=3.6',  # supported Python ranges
         install_requires=[
-            'psutil',
+            # psutil not supported on Windows, we haven't tested in other platforms, but since it's not essential
+            # to the functioning of Tarski, better be conservative here and install only on Linux.
+            'psutil; platform_system=="Linux"',
+
             'multipledispatch',
 
             # Antlr pinned to a specific version to avoid messages "ANTLR runtime and generated code versions disagree"

src/tarski/utils/resources.py

@@ -6,24 +6,39 @@
 import os
 import sys
 import time
-import psutil
+
+
+def get_mem_usage():
+    """ Return the memory usage as reported by psutil, or None, if the platform
+    does not support psutil, or """
+    try:
+        import psutil
+    except ImportError:
+        return None
+    return psutil.Process().memory_info().rss
 
 
 class Timer:
     def __init__(self):
         self.start_time = time.time()
         self.start_clock = self._clock()
-        self.start_mem = psutil.Process().memory_info().rss
+        self.start_mem = get_mem_usage()
 
     @staticmethod
     def _clock():
         times = os.times()
         return times[0] + times[1]
 
     def __str__(self):
-        current = psutil.Process().memory_info().rss
-        current_in_mb = current / (1024*1024)
-        rss_in_mb = (current - self.start_mem) / (1024*1024)
+        rss_in_mb = "-"
+        current_in_mb = "-"
+        if self.start_mem is not None:
+            # self.start_mem is None whenever the underlying platform could not import the psutil module,
+            # in which case at the moment we're happy simply not to show memory consumption info.
+            current = get_mem_usage()
+            current_in_mb = current / (1024*1024)
+            rss_in_mb = (current - self.start_mem) / (1024*1024)
+
         return "[%.2fs CPU, %.2fs wall-clock, diff: %.2fMB, curr:  %.2fMB]" % (
             self._clock() - self.start_clock,
             time.time() - self.start_time, rss_in_mb, current_in_mb)

tests/test_utils.py

@@ -0,0 +1,13 @@
+
+from tarski.utils import resources
+
+
+def test_timer_class():
+    # Some very exciting algorithms to exercise the timing functionality
+    x = 0
+    with resources.timing("\tHello world"):
+        x += 1
+    assert x == 1
+    with resources.timing("\tHello world", newline=True):
+        x += 1
+    assert x == 2