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You can use the dictionary constructor and implicit expansion to reconstruct a dictionary. Moreover, interestingly, this method can be used to control the positional order during dictionary construction (post Python 3.6). In fact, insertion order is guaranteed for Python 3.7 and above!
There are two ways to add one dictionary to another: Update (modifies orig in place) orig.update(extra) # Python 2.7+. orig |= extra # Python 3.9+. Merge (creates a new dictionary) # Python 2.7+. dest = collections.ChainMap(orig, extra) dest = {k: v for d in (orig, extra) for (k, v) in d.items()} # Python 3.
I want to build a dictionary in Python. However, all the examples that I see are instantiating a dictionary from a list, etc . ..
If you are not yet on Python 3.5 or need to write backward-compatible code, and you want this in a single expression, the most performant while the correct approach is to put it in a function: def merge_two_dicts (x, y): """Given two dictionaries, merge them into a new dict as a shallow copy.""" z = x.copy () z.update (y) return z.
to test if "one" is among the values of your dictionary. In Python 2, it's more efficient to use. "one" in d.itervalues() instead. Note that this triggers a linear scan through the values of the dictionary, short-circuiting as soon as it is found, so this is a lot less efficient than checking whether a key is present.
@OrsirisdeJong dict.keys(), etc are dictionary view objects and have been so in all Python 3 releases, not just since 3.6. Don’t turn those into a list, use next((k for k, v in dict.items() if v == search_age), None) to find a match.
In a function signature. *t means "take all additional positional arguments to this function and pack them into this parameter as a tuple." def foo(*t): print(t) >>> foo(1, 2) (1, 2) **d means "take all additional named arguments to this function and insert them into this parameter as dictionary entries." def foo(**d):
When you iterate through dictionaries using the for .. in .. -syntax, it always iterates over the keys (the values are accessible using dictionary[key]). To iterate over key-value pairs, use the following: for k,v in dict.iteritems() in Python 2. for k,v in dict.items() in Python 3.
8. This looks like homework, so I'll only provide a few hints. You probably know that this is how you create a new dictionary: d = {} Adding an entry to a dictionary: d[key] = value. More specifically, adding an entry whose key is a string and whose value is another dictionary: d["gymnasium"] = {}
You can find a dict index by counting into the dict.keys() with a loop. If you use the enumerate() function, it will generate the index values automatically. This is the most straight-forward, but costs a little more CPU every time you look up the index. This assumes an ordered dict (Python 3.7+ guarantees this).