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