Python dictionary example web code geeks – 2017 funny jokes for adults short


Now, let’s see how to retrieve a value from this dictionary. There are two ways of doing this: The known “[]” syntax where we write dict["key"] and get the result, or the dict.get("key", "default value") which also returns the result.

What’s the difference? Well, the [] syntax results in a KeyError if the key is not defined, and we usually don’t want that us stock futures cnn. The get method receives the key and an optional default value, and it does not result in any annoying error if the key is not found, it just returns None.

There it is, the key “this_one_does_not_exist” does not exist, so a KeyError is raised. Let’s put that KeyError in an except clause, and check the get method.

Here, we put the missing key in a try/except, which prints “KeyError” on failure. Then we see the get method examples, we ask for a key and return a default message if it’s not found.

The output: [‘dog’, ‘cat’, ‘fish’]

Dictionaries are mutable data structures usd to sgd converter. We can add keys to it, update their values and even delete them. Let’s see one by one in our example:

EXAMPLE_DICT["this_one_does_not_exist"] = "it exists now" # This statement will create the key "this_one_does_not_exist" and assign to it the value "it exists now"

There is a method called print_key which receives a dictionary and a key. It prints the value of the given key in the given dictionary or “Key was not found” instead.

We are creating the key this_one_does_not_exist first, and printing it out. Then we are updating a_boolean and also printing it binary to decimal converter. At last, we delete this_one_does_not_exist from the dict and print it again. The result: it exists now

It works as expected. Notice that, in the context of writing a key, the [] syntax doesn’t throw an error if the key was not found, so in this case you can use it without worrying. 4. Useful operations

The in keyword is a tool Python provides to, in this case, check whether a key is present in a dictionary or not. Let’s make our own implementation of the get method to test this keyword:

Withing our custom get method, we use the [] syntax to retrieve the requested key from the given dictionary, but not without checking if the key is present there with the in keyword euro forecast model. We receive a default value which by default is None. It behaves exactly like the native get method, here is the output: Sebastián

This tool can also be used to iterate over the dictionary keys, let’s implement a method which returns an array with all the keys in a dictionary to see it working:

It’s pretty simple, right? In human language, that iterates for every key in the given dictionary and returns an array with them. The output: [‘name’, ‘age’]

The len function returns the number of key-value pairs in a dictionary. It’s data types do not matter in this context. Notice the fact that it returns the number of key-value pairs, so a dictionary that looks like {"key", "value"} will return 1 when asked for its length.

Its use is pretty simple, it receives the dictionary in question as argument, and just for testing purposes we’ll modify the to check that the number of keys its returning is the same as the len of the dict.

There is the check, if we uncomment the second line of the function’s body we’ll see the exception raised: Traceback (most recent call last):

The message Exception: expected 2 keys. got 3 is telling us that the keys we are about to return contain an extra key us dollar to canadian dollar chart. This is another useless but explicit example. 4.3. keys() and values()

Let’s see a couple functions that render obsolete the function keys we just wrote. These are keys() and values() stock market cnn news. I think it’s pretty intuitive what these functions do, keys returns every key in the dictionary and values returns every value in the dictionary.

Having a dictionary like me = {"name": "Sebastián", "age": 21}, me.keys() will return ["name", "age"] and me.values() will return ["Sebastián", 21]. Kind of… see, dictionaries in python are not ordered, then, the result of keys and values aren’t either. If you need to sort either keys or values just call sorted passing the array as argument.

Here we are creating a dictionary containing some keys, and then iterating over the keys and values to print them out. I know it’s not the prettiest code but it proves my point. When we execute it one time we see: age: 21

See? That’s because dictionaries’ keys are not sorted, to solve this issue (and fix that awful piece of code) let’s change that script a little bit. We won’t be using the function values anymore since it’s not necessary, but I think it’s pretty clear the way to use it.

Now, why am I giving so much importance to the lack of sorting of dictionaries? Well, imagine you are storing it in a CSV file binary sms. Every time you write a dictionary, as the keys are in arbitrary orders, the CSV’s rows won’t be consistent, and it will mess up your program by writing each row with the columns in different orders. So when you need your data in a strict order, please keep in mind this little fact. 4.4. items()

This method returns a list of tuples containing every key-value pair in the dictionary as ({"a": 1, "b": 2}.items() => [("a", 1), ("b", 2)]). With this method we can iterate over this pair array more seamlessly (keep in mind that this is still unordered), so if we just want to print our dictionary and the order doesn’t matter we can write:

This will output the same as the first, “key: value” with different orders in each execution. Something to notice is the fact that we can not assign new values to tuples. We access values in tuples by tuple[0] and tuple[1], but we can’t do tuepl[0] = 1 exchange rate usd to inr history. This will rase a TypeError: ‘tuple’ object does not support item assignment. 4.5. update()

This method changes one dictionary to have new values from a second one nzd vs usd forecast. It modifies existing values, as dictionaries are mutable (keep this in mind). Let’s see an example:

Here we are printing the product, executing sell a hundred times and then printing the product again. The sell function updates de product subtracting one from “stock” and adding one to “sold”. The output: description: WCG E-Book, price: 2.75, sold: 1500, stock: 5700

Notice that we don’t return a new dictionary with the updated values, it updates the existing one. This is an easy way of updating a couple keys in a dictionary without having to overwrite them one by one. 4.6. copy()

A dictionary’s copy method will copy the entire dictionary into a new one. One thing to notice is that it’s a shallow copy. If you have nested dictionaries, it will copy the first level, but the inner dictionaries will be a reference to the same object. Let’s see an example:

In this script, we are creating a dictionary with some data and then copying it. We change the clone’s age and print both, and then do the same with the first names.

Now, my clone is a copy of me, it is not a reference to the same memory address, so if I change its age, mine will remain the same. But, the inner dictionary, the one containing the name, is a reference to the same memory address, when I change my clone’s name, mine will change too usd to pound conversion. Let’s see the output: my age: 21, my clone’s age: 22

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