Source start dates are soft limits.

src/pricehist/cli.py

@@ -88,6 +88,12 @@ def cmd_fetch(args):
     output = outputs.by_type[args.output]()
     start = args.start or source.start()
 
+    if start < source.start():
+        logging.warn(
+            f"The start date {start} preceeds the {source.name()} "
+            f"source start date of {source.start()}."
+        )
+
     prices = source.fetch(args.pair, args.type, start, args.end)
 
     if args.renamebase or args.renamequote:

src/pricehist/sources/coindesk.py

@@ -51,13 +51,6 @@ class CoinDesk:
     def fetch(self, pair, type, start, end):
         base, quote = pair.split("/")
 
-        min_start = self.start()
-        if start < min_start:
-            exit(
-                f"start {start} too early. The CoinDesk BPI only covers data"
-                f"from {min_start} onwards."
-            )
-
         url = "https://api.coindesk.com/v1/bpi/historical/close.json"
         params = {
             "currency": quote,

src/pricehist/sources/ecb.py

@@ -49,10 +49,6 @@ class ECB:
     def fetch(self, pair, type, start, end):
         base, quote = pair.split("/")
 
-        min_start = self.start()
-        if start < min_start:
-            exit(f"start {start} too early. Minimum is {min_start}")
-
         almost_90_days_ago = str(datetime.now().date() - timedelta(days=85))
         data = self._raw_data(start < almost_90_days_ago)
         root = etree.fromstring(data)