chore: add default head/tail

Author: ion-elgreco

python/datafusion/dataframe.py

@@ -223,7 +223,7 @@ def limit(self, count: int, offset: int = 0) -> DataFrame:
         """
         return DataFrame(self.df.limit(count, offset))
 
-    def head(self, n: int) -> DataFrame:
+    def head(self, n: int = 5) -> DataFrame:
         """Return a new :py:class:`DataFrame` with a limited number of rows.
 
         Args:
@@ -234,10 +234,11 @@ def head(self, n: int) -> DataFrame:
         """
         return DataFrame(self.df.limit(n, 0))
 
-    def tail(self, n: int) -> DataFrame:
+    def tail(self, n: int = 5) -> DataFrame:
         """Return a new :py:class:`DataFrame` with a limited number of rows.
 
-        Be aware this could be potentially expensive due to the size of the frame.
+        Be aware this could be potentially expensive since the row size needs to be
+        determined of the dataframe. This is done by collecting it.
 
         Args:
             n: Number of rows to take from the tail of the DataFrame.