diff --git a/src/pricehist/cli.py b/src/pricehist/cli.py
index 53b7f92..8909a5b 100644
--- a/src/pricehist/cli.py
+++ b/src/pricehist/cli.py
@@ -1,5 +1,4 @@
 import argparse
-import sys
 from datetime import datetime, timedelta
 
 from pricehist import outputs, sources
@@ -37,7 +36,6 @@ def cmd_source(args):
 
 def cmd_fetch(args):
     source = sources.by_id[args.source]()
-    start = args.start or args.after
     output = outputs.by_type[args.output]()
     prices = source.fetch(args.pair, args.start, args.end)
     print(output.format(prices))
@@ -66,7 +64,7 @@ def build_parser():
 
     subparsers = parser.add_subparsers(title="commands", dest="command")
 
-    sources_parser = subparsers.add_parser("sources", help="list sources")
+    subparsers.add_parser("sources", help="list sources")
 
     source_parser = subparsers.add_parser("source", help="show source details")
     source_parser.add_argument(
diff --git a/src/pricehist/outputs/beancount.py b/src/pricehist/outputs/beancount.py
index 9ef9c93..f8c5c9f 100644
--- a/src/pricehist/outputs/beancount.py
+++ b/src/pricehist/outputs/beancount.py
@@ -2,7 +2,6 @@ class Beancount:
     def format(self, prices):
         lines = []
         for price in prices:
-            date = str(price.date).translate(str.maketrans("-", "/"))
             lines.append(
                 f"{price.date} price {price.base} {price.amount} {price.quote}"
             )
diff --git a/src/pricehist/outputs/csv.py b/src/pricehist/outputs/csv.py
index 0dec50d..9b457d8 100644
--- a/src/pricehist/outputs/csv.py
+++ b/src/pricehist/outputs/csv.py
@@ -2,7 +2,6 @@ class CSV:
     def format(self, prices):
         lines = ["date,base,quote,amount"]
         for price in prices:
-            date = str(price.date).translate(str.maketrans("-", "/"))
             line = ",".join([price.date, price.base, price.quote, str(price.amount)])
             lines.append(line)
         return "\n".join(lines)
diff --git a/src/pricehist/outputs/gnucashsql.py b/src/pricehist/outputs/gnucashsql.py
index 450b22c..9d838c5 100644
--- a/src/pricehist/outputs/gnucashsql.py
+++ b/src/pricehist/outputs/gnucashsql.py
@@ -21,7 +21,18 @@ class GnuCashSQL:
             guid = m.hexdigest()[0:32]
             value_num = str(price.amount).replace(".", "")
             value_denom = 10 ** len(f"{price.amount}.".split(".")[1])
-            v = f"('{guid}', '{date}', '{price.base}', '{price.quote}', '{source}', '{typ}', {value_num}, {value_denom})"
+            v = (
+                "("
+                f"'{guid}', "
+                f"'{date}', "
+                f"'{price.base}', "
+                f"'{price.quote}', "
+                f"'{source}', "
+                f"'{typ}', "
+                f"{value_num}, "
+                f"{value_denom}"
+                ")"
+            )
             values.append(v)
 
         comma_newline = ",\n"
diff --git a/src/pricehist/sources/coindesk.py b/src/pricehist/sources/coindesk.py
index 42ada10..8af5884 100644
--- a/src/pricehist/sources/coindesk.py
+++ b/src/pricehist/sources/coindesk.py
@@ -17,7 +17,10 @@ class CoinDesk:
 
     @staticmethod
     def description():
-        return "An average of bitcoin prices across leading global exchanges. Powered by CoinDesk, https://www.coindesk.com/price/bitcoin"
+        return (
+            "An average of bitcoin prices across leading global exchanges. "
+            "Powered by CoinDesk, https://www.coindesk.com/price/bitcoin"
+        )
 
     @staticmethod
     def source_url():
@@ -45,11 +48,17 @@ class CoinDesk:
         min_start = "2010-07-17"
         if start < min_start:
             exit(
-                f"start {start} too early. The CoinDesk BPI only covers data from {min_start} onwards."
+                f"start {start} too early. The CoinDesk BPI only covers data"
+                f"from {min_start} onwards."
             )
 
-        url = f"https://api.coindesk.com/v1/bpi/historical/close.json?currency={quote}&start={start}&end={end}"
-        response = requests.get(url)
+        url = "https://api.coindesk.com/v1/bpi/historical/close.json"
+        params = {
+            "currency": quote,
+            "start": start,
+            "end": end,
+        }
+        response = requests.get(url, params=params)
         data = json.loads(response.content)
         prices = []
         for (d, v) in data["bpi"].items():
diff --git a/src/pricehist/sources/coinmarketcap.py b/src/pricehist/sources/coinmarketcap.py
index cee4482..118799a 100644
--- a/src/pricehist/sources/coinmarketcap.py
+++ b/src/pricehist/sources/coinmarketcap.py
@@ -1,7 +1,6 @@
 import json
-from datetime import datetime, timedelta
+from datetime import datetime
 from decimal import Decimal
-from xml.etree import ElementTree
 
 import requests
 
@@ -25,9 +24,10 @@ class CoinMarketCap:
     def source_url():
         return "https://coinmarketcap.com/"
 
-    # # currency metadata - these may max out at 5k items (crypto data is currently 4720 items)
-    # curl 'https://web-api.coinmarketcap.com/v1/fiat/map?include_metals=true' | jq . | tee fiat-map.json
-    # curl 'https://web-api.coinmarketcap.com/v1/cryptocurrency/map' | jq . | tee cryptocurrency-map.json
+    # # currency metadata - these may max out at 5k items
+    # #   (crypto data is currently 4720 items)
+    # curl '.../v1/fiat/map?include_metals=true' | jq . | tee fiat-map.json
+    # curl '.../v1/cryptocurrency/map' | jq . | tee cryptocurrency-map.json
 
     @staticmethod
     def bases():
@@ -40,13 +40,14 @@ class CoinMarketCap:
     def fetch(self, pair, start, end):
         base, quote = pair.split("/")
 
-        url = f"https://web-api.coinmarketcap.com/v1/cryptocurrency/ohlcv/historical"
+        url = "https://web-api.coinmarketcap.com/v1/cryptocurrency/ohlcv/historical"
         params = {
             "symbol": base,
             "convert": quote,
             "time_start": int(datetime.strptime(start, "%Y-%m-%d").timestamp()),
-            "time_end": int(datetime.strptime(end, "%Y-%m-%d").timestamp())
-            + 24 * 60 * 60,  # round up to include the last day
+            "time_end": (
+                int(datetime.strptime(end, "%Y-%m-%d").timestamp()) + 24 * 60 * 60
+            ),  # round up to include the last day
         }
 
         response = requests.get(url, params=params)
diff --git a/src/pricehist/sources/ecb.py b/src/pricehist/sources/ecb.py
index 3fb0355..1efe952 100644
--- a/src/pricehist/sources/ecb.py
+++ b/src/pricehist/sources/ecb.py
@@ -1,4 +1,3 @@
-import json
 from datetime import datetime, timedelta
 from decimal import Decimal
 from xml.etree import ElementTree
@@ -78,10 +77,11 @@ class ECB:
             exit(f"start {start} too early. Minimum is {min_start}")
 
         almost_90_days_ago = str(datetime.now().date() - timedelta(days=85))
+        url_base = "https://www.ecb.europa.eu/stats/eurofxref"
         if start > almost_90_days_ago:
-            source_url = "https://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist-90d.xml"  # last 90 days
+            source_url = f"{url_base}/eurofxref-hist-90d.xml"  # last 90 days
         else:
-            source_url = "https://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist.xml"  # since 1999
+            source_url = f"{url_base}/eurofxref-hist.xml"  # since 1999
 
         response = requests.get(source_url)
         data = response.content
@@ -96,7 +96,8 @@ class ECB:
         for day in root.find("default:Cube", namespaces):
             date = day.attrib["time"]
             rate_xpath = f"./*[@currency='{quote}']"
-            # TODO what if it's not found for that day? (some quotes aren't in the earliest data)
+            # TODO what if it's not found for that day?
+            # (some quotes aren't in the earliest data)
             rate = Decimal(day.find(rate_xpath).attrib["rate"])
             all_rows.insert(0, (date, rate))
         selected = [