ex3.7

reader.py

@@ -1,5 +1,6 @@
 import collections.abc
 import csv
+from abc import ABC, abstractmethod
 
 
 class DataCollection(collections.abc.Sequence):
@@ -30,16 +31,48 @@ class DataCollection(collections.abc.Sequence):
             self.data[name].append(d[name])
 
 
+class CSVParser(ABC):
+    def parse(self, filename):
+        records = []
+        with open(filename) as f:
+            rows = csv.reader(f)
+            headers = next(rows)
+            for row in rows:
+                records.append(self.make_record(headers, row))
+        return records
+
+    @abstractmethod
+    def make_record(self, headers, row):
+        pass
+
+
+class DictCSVParser(CSVParser):
+    def __init__(self, types):
+        self.types = types
+
+    def make_record(self, headers, row):
+        return {name: func(val) for name, func, val in zip(headers, self.types, row)}
+
+
+class InstanceCSVParser(CSVParser):
+    def __init__(self, cl):
+        self.cls = cl
+
+    def make_record(self, headers, row):
+        return self.cls.from_row(row)
+
+
 def read_csv_as_dicts(filename, conversions):
-    value = []
-    with open(filename) as f:
-        rows = csv.reader(f)
-        headers = next(rows)
-        for row in rows:
-            value.append(
-                {name: func(val) for name, func, val in zip(headers, conversions, row)}
-            )
-    return value
+    parser = DictCSVParser(conversions)
+    records = parser.parse(filename)
+    return records
+
+
+def read_csv_as_instances(filename, cls):
+    """Read a CSV file into a list of instances"""
+    parser = InstanceCSVParser(cls)
+    records = parser.parse(filename)
+    return records
 
 
 def read_csv_as_columns(filename, conversions):
@@ -52,14 +85,3 @@ def read_csv_as_columns(filename, conversions):
                 {name: func(val) for name, func, val in zip(headers, conversions, row)}
             )
     return value
-
-
-def read_csv_as_instances(filename, cls):
-    """Read a CSV file into a list of instances"""
-    records = []
-    with open(filename) as f:
-        rows = csv.reader(f)
-        _ = next(rows)
-        for row in rows:
-            records.append(cls.from_row(row))
-    return records

tableformat.py

@@ -1,12 +1,17 @@
-class TableFormatter:
+from abc import ABC, abstractmethod
+
+
+class TableFormatter(ABC):
+    @abstractmethod
     def headings(self, headers):
-        raise NotImplementedError()
+        pass
 
+    @abstractmethod
     def row(self, rowdata):
-        raise NotImplementedError()
+        pass
 
 
-class TextTableFormatter:
+class TextTableFormatter(TableFormatter):
     def _printer(self, data):
         print(*("{: >10}".format(value) for value in data))
 
@@ -18,7 +23,7 @@ class TextTableFormatter:
         self._printer(rowdata)
 
 
-class CSVTableFormatter:
+class CSVTableFormatter(TableFormatter):
     def _printer(self, data):
         print(",".join(str(value) for value in data))
 
@@ -29,7 +34,7 @@ class CSVTableFormatter:
         return self._printer(rowdata)
 
 
-class HTMLTableFormatter:
+class HTMLTableFormatter(TableFormatter):
     def _cell(self, value, tag):
         return f"<{tag}>{value}</{tag}>"
 
@@ -57,6 +62,9 @@ def create_formatter(name):
 
 
 def print_table(records, fields, formatter):
+    if not isinstance(formatter, TableFormatter):
+        raise TypeError("expected a TableFormatter")
+
     formatter.headings(fields)
     for record in records:
         formatter.row([getattr(record, fieldname) for fieldname in fields])