Remove arrow. Fixes #120.

ocelot/transformations/uncertainty/pedigree.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-import arrow
+from datetime import datetime
 
 
 PEDIGREE_MATRIX_VALUES = {
@@ -32,12 +32,32 @@ def get_pedigree_variance(pm, version="original"):
     return sum(PEDIGREE_MATRIX_VALUES[version][k][v - 1] for k, v in pm.items())
 
 
+def get_difference_in_years(first, second):
+    """Get absolute value of difference in years between ``first`` and ``second``.
+
+    Input values can be integers, or datetime strings like "2002-12-31". Only uses the year of a datetime string, and no rounding, so the difference between "2002-01-01" and "2002-12-31" is zero.
+
+    Returns an integer.
+
+    """
+    year = lambda x: x if isinstance(x, int) else datetime.strptime(x, "%Y-%m-%d").year
+    return abs(year(first) - year(second))
+
+
 def adjust_pedigree_matrix_time(ds, exc, year):
+    """Adjust values of ``temporal correlation`` in the pedigree matrix of exchange ``exc`` to a new year ``year``.
+
+    Does nothing if pedigree matrix not present in exchange.
+
+    Datasets are defined for a certain temporal period. If the baseline year is outside that period, the values of ``temporal correlation`` need to be modified to adjust the increased uncertainty that comes from applying the dataset to a different year. Modified numbers from a table provided by IFU Hamburg.
+
+    Modifies the exchange in place, and returns the modified exchange.
+
+    """
     if 'pedigree matrix' not in exc:
         return exc
 
-    new_year = year if isinstance(year, int) else arrow.get(year).year
-    difference = new_year - arrow.get(ds['end date']).year
+    difference = get_difference_in_years(ds['end date'], year)
     current_value = exc['pedigree matrix']['temporal correlation']
 
     if difference > 0:

setup.py

@@ -38,7 +38,6 @@ def package_files(directory):
     },
     install_requires=[
         'appdirs',
-        'arrow',
         'bw2parameters',
         'docopt',
         'docutils',

tests/uncertainty/pedigree.py

@@ -6,6 +6,8 @@
 apmt = adjust_pedigree_matrix_time
 
 
+### Test changing pedigree matrix variance
+
 def test_get_pedigree_variance_error():
     matrix = {
         "reliability": 1,
@@ -36,6 +38,20 @@ def test_get_pedigree_variance_no_keys():
 def test_adjust_pedigree_matrix_time_no_pm():
     assert apmt(None, {}, None) == {}
 
+
+### Test changing pedigree matrix temporal correlation
+
+def test_get_difference_in_years():
+    a = "2002-12-31"
+    b = "2002-01-01"
+    c = "2012-01-31"
+    assert get_difference_in_years(a, b) == 0
+    assert get_difference_in_years(b, a) == 0
+    assert get_difference_in_years(b, c) == 10
+    assert get_difference_in_years(c, a) == 10
+    assert get_difference_in_years(2006, a) == 4
+
+
 def test_adjust_pedigree_matrix_time():
     def ds_and_exc(current=0):
         return {'end date': '2000-01-01'}, {'pedigree matrix': {'temporal correlation': current}}