completed dict examples by adding various methods for initialising, for example with defaultdict

python_3_oop/chapter06/dicts.py

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+from collections import defaultdict
+
+
+stocks = {"GOOG": (613.30, 625.86, 610.50),
+          "MSFT": (30.25, 30.70, 30.19)}
+
+# different possibilities to get values from the dictionary
+print("GOOG: {}".format(stocks["GOOG"]))
+print("RIM: {}".format(stocks.get("RIM", "NOT FOUND")))
+stocks.setdefault("RIM", (67.38, 68.48, 67.28))
+print("RIM: {}".format(stocks["RIM"]))
+
+for stock, values in stocks.items():
+    print("{} last value is {}".format(stock, values[0]))
+
+random_keys = {}
+random_keys["astring"] = "somestring"
+random_keys[5] = "aninteger"
+random_keys[25.2] = "floats work too"
+random_keys[("abc", 123)] = "so do tuples"
+
+
+class AnObject(object):
+
+    def __init__(self, avalue):
+        self.avalue = avalue
+
+
+my_object = AnObject(14)
+random_keys[my_object] = "We can even store objects"
+my_object.avalue = 12
+
+try:
+    random_keys[[1, 2, 3]] = "We can't store lists though"
+except:
+    print("unable to store list \n")
+
+for key, value in random_keys.items():
+    print("{} has value {}".format(key, value))
+    if hasattr(key, "avalue"):
+        print("{}.avalue ={}".format(key, key.avalue))
+
+
+def letter_frequency(sentence):
+    frequencies = {}
+    for letter in sentence:
+        frequency = frequencies.setdefault(letter, 0)
+        frequencies[letter] = frequency + 1
+    return frequencies
+
+print(letter_frequency("Hello world, what's going on?"))
+
+
+# defaultdict using built-in function
+def letter_frequency_defdict(sentence):
+    frequencies = defaultdict(int)
+    for letter in sentence:
+        frequencies[letter] += 1
+    return frequencies
+
+print(letter_frequency_defdict("Hello world, what's going on?"))
+
+
+# defaultdict using self defined function
+num_items = 0
+
+
+def tuple_counter():
+    global num_items
+    num_items += 1
+    return num_items, []
+
+d = defaultdict(tuple_counter)
+
+d['a'][1].append("hello")
+d['b'][1].append("world")
+
+print(d)