specify user-agent in tmy3 remote request (#494)

Closes #493

Author: wholmgren

docs/sphinx/source/whatsnew/v0.6.0.rst

@@ -23,6 +23,8 @@ Bug fixes
   (:issue:`464`)
 * ModelChain.prepare_inputs failed to pass solar_position and airmass to
   Location.get_clearsky. Fixed. (:issue:`481`)
+* Add User-Agent specification to TMY3 remote requests to avoid rejection.
+  (:issue:`493`)
 
 
 Documentation

pvlib/tmy.py

@@ -7,9 +7,9 @@
 import dateutil
 import io
 try:
-    from urllib2 import urlopen
+    from urllib2 import urlopen, Request
 except ImportError:
-    from urllib.request import urlopen
+    from urllib.request import urlopen, Request
 
 import pandas as pd
 
@@ -164,14 +164,23 @@ def readtmy3(filename=None, coerce_year=None, recolumn=True):
 
     head = ['USAF', 'Name', 'State', 'TZ', 'latitude', 'longitude', 'altitude']
 
-    try:
-        csvdata = open(filename, 'r')
-    except IOError:
-        response = urlopen(filename)
+    if filename.startswith('http'):
+        request = Request(filename, headers={'User-Agent':
+            'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_5) '
+            'AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.87 '
+            'Safari/537.36'})
+        response = urlopen(request)
         csvdata = io.StringIO(response.read().decode(errors='ignore'))
+    else:
+        # assume it's accessible via the file system
+        csvdata = open(filename, 'r')
+
+    # read in file metadata, advance buffer to second line
+    firstline = csvdata.readline()
+    if 'Request Rejected' in firstline:
+        raise IOError('Remote server rejected TMY file request')
 
-    # read in file metadata
-    meta = dict(zip(head, csvdata.readline().rstrip('\n').split(",")))
+    meta = dict(zip(head, firstline.rstrip('\n').split(",")))
 
     # convert metadata strings to numeric types
     meta['altitude'] = float(meta['altitude'])
@@ -180,8 +189,12 @@ def readtmy3(filename=None, coerce_year=None, recolumn=True):
     meta['TZ'] = float(meta['TZ'])
     meta['USAF'] = int(meta['USAF'])
 
+    # use pandas to read the csv file/stringio buffer
+    # header is actually the second line in file, but tell pandas to look for
+    # header information on the 1st line (0 indexing) because we've already
+    # advanced past the true first line with the readline call above.
     data = pd.read_csv(
-        filename, header=1,
+        csvdata, header=0,
         parse_dates={'datetime': ['Date (MM/DD/YYYY)', 'Time (HH:MM)']},
         date_parser=lambda *x: _parsedate(*x, year=coerce_year),
         index_col='datetime')