cleaning up and organizing old problems (builtin)

src/USEFUL/advanced/lru_cache.py

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+#!/usr/bin/env python3
+
+__author__ = "bt3"
+
+
+from functools import lru_cache
+
+
+@lru_cache(maxsize=20)
+def fib(n):
+    if n < 2:
+        return n
+    return fib(n-1) + fib(n-2)
+
+
+if __name__ == '__main__':
+    print([fib(n) for n in range(10)])
+    print(fib.cache_info())

src/USEFUL/basic_examples/example_OrderedDict.py

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+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+from collections import OrderedDict
+
+def  OrderedDict_example():
+    ''' show some examples for OrderedDict '''
+    ''' keep the order of insertion.
+        maintains a doubly linked list, so size is more than twice than normal dict'''
+
+
+    pairs = [('a', 1), ('b',2), ('c',3)]
+
+    d1 = {}
+    for key, value in pairs:
+        if key not in d1:
+            d1[key] = []
+        d1[key].append(value)
+    for key in d1:
+        print(key, d1[key])
+
+    d2 = OrderedDict(pairs)
+    for key in d2:
+        print(key, d2[key])
+
+
+if __name__ == '__main__':
+    OrderedDict_example()
+
+

src/USEFUL/basic_examples/example_counter.py

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+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+from collections import Counter
+
+def  Counter_example():
+    ''' it is a dictionary that maps the items to the number of occurrences '''
+    seq1 = [1, 2, 3, 5, 1, 2, 5, 5, 2, 5, 1, 4]
+    seq_counts = Counter(seq1)
+    print(seq_counts)
+
+    ''' we can increment manually or use the update() method '''
+    seq2 = [1, 2, 3]
+    seq_counts.update(seq2)
+    print(seq_counts)
+
+    seq3 = [1, 4, 3]
+    for key in seq3:
+        seq_counts[key] += 1
+    print(seq_counts)
+
+    ''' also, we can use set operations such as a-b or a+b '''
+    seq_counts_2 = Counter(seq3)
+    print(seq_counts_2)
+    print(seq_counts + seq_counts_2)
+    print(seq_counts - seq_counts_2)
+
+if __name__ == '__main__':
+    Counter_example()
+
+

src/USEFUL/basic_examples/example_defaultdict.py

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+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+from collections import defaultdict
+
+def  defaultdict_example():
+    ''' show some examples for defaultdicts '''
+    pairs = {('a', 1), ('b',2), ('c',3)}
+
+    d1 = {}
+    for key, value in pairs:
+        if key not in d1:
+            d1[key] = []
+        d1[key].append(value)
+    print(d1)
+
+    d2 = defaultdict(list)
+    for key, value in pairs:
+        d2[key].append(value)
+    print(d2)
+
+
+if __name__ == '__main__':
+    defaultdict_example()
+
+

src/USEFUL/basic_examples/example_setdefault.py

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+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+def usual_dict(dict_data):
+    newdata = {}
+    for k, v in dict_data:
+        if k in newdata:
+            newdata[k].append(v)
+        else:
+            newdata[k] = [v]
+    return newdata
+
+
+def setdefault_dict(dict_data):
+    newdata = {}
+    for k, v in dict_data:
+        newdata.setdefault(k, []).append(v)
+    return newdata
+
+
+def test_setdef(module_name='this module'):
+    dict_data = (('key1', 'value1'),
+               ('key1', 'value2'),
+               ('key2', 'value3'),
+               ('key2', 'value4'),
+               ('key2', 'value5'),)
+    print(usual_dict(dict_data))
+    print(setdefault_dict(dict_data))
+
+    s = 'Tests in {name} have {con}!'
+    print(s.format(name=module_name, con='passed'))
+
+
+if __name__ == '__main__':
+    test_setdef()
+