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Exercises/soln3_7.md

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+# Exercise 3.7 - Solution
+
+## (a) Interfaces
+
+```python
+# tableformat.py
+
+def print_table(records, fields, formatter):
+    if not isinstance(formatter, TableFormatter):
+        raise TypeError('Expected a TableFormatter')
+
+    formatter.headings(fields)
+    for r in records:
+        rowdata = [getattr(r, fieldname) for fieldname in fields]
+        formatter.row(rowdata)
+...
+```
+
+## (b) Abstract Base Classes
+
+```python
+# tableformat.py
+from abc import ABC, abstractmethod
+
+class TableFormatter(ABC):
+    @abstractmethod
+    def headings(self, headers):
+        pass
+
+    @abstractmethod
+    def row(self, rowdata):
+        pass
+```
+
+## (c) Algorithm Template Classes
+
+```python
+# reader.py
+
+import csv
+from abc import ABC, abstractmethod
+
+class CSVParser(ABC):
+    def parse(self, filename):
+        records = []
+        with open(filename) as f:
+            rows = csv.reader(f)
+            headers = next(rows)
+            for row in rows:
+                record = self.make_record(headers, row)
+                records.append(record)
+        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, cls):
+        self.cls = cls
+
+    def make_record(self, headers, row):
+        return self.cls.from_row(row)
+
+def read_csv_as_dicts(filename, types):
+    parser = DictCSVParser(types)
+    return parser.parse(filename)
+
+def read_csv_as_instances(filename, cls):
+    parser = InstanceCSVParser(cls)
+    return parser.parse(filename)
+```
+
+
+
+
+[Back](ex3_7.md)