txns: Uses sp.min_fee if available (#530)

* Uses sp.min_fee if available

Rather than use a hard coded constant for min_fee, use the one that is
returned in SuggestedParams if available.

Since some people may create a SuggestedParams by hand rather than get
one from server (because our APIs require one even though the caller
may feel they "know better"), continue to use the constant if the
sp.min_fee is None.

* Only use the constant if sp.min_fee is None (not when 0)

algosdk/transaction.py

@@ -368,9 +368,8 @@ def __init__(
             raise error.WrongAmountType
         self.close_remainder_to = close_remainder_to
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     def dictify(self):
         d = dict()
@@ -480,9 +479,8 @@ def __init__(
         self.sprfkey = self._fixed_bytes64(sprfkey, 64)
 
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     def dictify(self):
         d = {}
@@ -866,9 +864,8 @@ def __init__(
         if self.decimals < 0 or self.decimals > constants.max_asset_decimals:
             raise error.OutOfRangeDecimalsError
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     def dictify(self):
         d = dict()
@@ -1221,9 +1218,8 @@ def __init__(
         self.target = target
         self.new_freeze_state = new_freeze_state
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     def dictify(self):
         d = dict()
@@ -1339,9 +1335,8 @@ def __init__(
         self.close_assets_to = close_assets_to
         self.revocation_target = revocation_target
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     def dictify(self):
         d = dict()
@@ -1612,9 +1607,8 @@ def __init__(
             boxes, self.foreign_apps, self.index
         )
         if not sp.flat_fee:
-            self.fee = max(
-                self.estimate_size() * self.fee, constants.min_txn_fee
-            )
+            mf = constants.min_txn_fee if sp.min_fee is None else sp.min_fee
+            self.fee = max(self.estimate_size() * self.fee, mf)
 
     @staticmethod
     def state_schema(schema):