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Exercises/soln5_3.md

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+# Exercise 5.3 - Solution
+
+## (a) Higher order functions
+
+```python
+# reader.py
+
+import csv
+
+def convert_csv(lines, converter, *, headers=None):
+    records = []
+    rows = csv.reader(lines)
+    if headers is None:
+        headers = next(rows)
+    for row in rows:
+        record = converter(headers, row)
+        records.append(record)
+    return records
+
+def csv_as_dicts(lines, types, *, headers=None):
+    return convert_csv(lines, 
+                       lambda headers, row: { name: func(val) for name, func, val in zip(headers, types, row) })
+
+def csv_as_instances(lines, cls, *, headers=None):
+    return convert_csv(lines,
+                       lambda headers, row: cls.from_row(row))
+
+def read_csv_as_dicts(filename, types, *, headers=None):
+    '''
+    Read CSV data into a list of dictionaries with optional type conversion
+    '''
+    with open(filename) as file:
+        return csv_as_dicts(file, types, headers=headers)
+
+def read_csv_as_instances(filename, cls, *, headers=None):
+    '''
+    Read CSV data into a list of instances
+    '''
+    with open(filename) as file:
+        return csv_as_instances(file, cls, headers=headers)
+```
+
+## (b) Using map()
+
+```python
+# reader.py
+
+import csv
+
+def convert_csv(lines, converter, *, headers=None):
+    records = []
+    rows = csv.reader(lines)
+    if headers is None:
+        headers = next(rows)
+    return map(lambda row: converter(headers, row), rows)
+```
+
+
+
+[Back](ex5_3.md)