# Understanding Dictionaries in Python

Dictionaries are a really essential concept for coding in Python. They are often used in places where you need to store a massive collection of data which is organized in a particular order (post Python 3.6).

Dictionaries commonly follow a *key-value* pair format. This is similar to hash maps in common data structures. 

### 1. Declaration

Dictionaries open and close with *keys* and *values* contained inside curly brackets. They can be declared in the following way:

```
sampleDict = {
    "name": "Sam",
    "age": "19",
}
```

This gives you a dictionary called `sampleDict` which stores, for example, the general information of a person.

### 2. Accessing Data

You can reference and access data stored in multiple ways. One way to do so would be the following way:

```
print(sampleDict["name"])
```

Displays the *value* of the *key* `name`:

```
Sam
```

You can also access data by assigning `sampleDict["name"]` to a variable and printing the variable such as follows:

```
x = sampleDict["name"]
print(x)
```

This would display the *value* of the 'name'. Similar to the code above.

```
Sam
```

Another way to access data is to use the `get()` method:

```
x = sampleDict.get("name")
print(x)
```

If you want just a list of all keys in the dictionary, the `key()` method returns a list of all the keys.

```
print(sampleDict.keys())
```

The output is as follows:

```
dict_keys(["name", "age"])
```

Similarly, if you want a list of all values in a dictionary, `values()` method can be used:

```
print(sampleDict.values())
```

Gives you the output:

```
dict_values(["Sam", "19"])
```

### 3. Adding and Deleting Data

There will be occasions where you will want to modify the contents of a dictionary. Sometimes, you will need to add new information and sometimes, you'll want to delete old information. 

To add new data, you declare a new key and assign a value to it:

```
sampleDict["school"] = "XYZ"
```

The modified dictionary looks like this:

```
sampleDict = {
    "name": "Sam",
    "age": "19",
    "school": "XYZ"
}
```

Another way to achieve the same result would be to use the `update()` method:

```
sampleDict.update({"school": "XYZ"})
```

The `update()` method could also be used to update the dictionary keys with new arguments.

To remove a specific key, you can use the `pop()` method:

```
sampleDict.pop("school")
print(sampleDict)
```

The dictionary will then look something like this:

```
sampleDict = {
    "name": "Sam",
    "age": "19",
}
```

Another way to delete the `school` key is to use the `del` keyword.

```
del sampleDict["school"]
```

### 4. Modifying Data

You can modify a key by referencing it along with the new value:

```
sampleDict = {
    "name": "Sam",
    "age": "19",
}
sampleDict["school"] = "XYZ"
print(sampleDict)
```

The dictionary will have the new key:

```
sampleDict = {
    "name": "Sam",
    "age": "19",
    "school": "XYZ"
}
```

Another way to update an item is to use the `update()` method. The code is the same as mentioned above.

### 5. Common Methods

`clear()` is used to clear the all the elements from a dictionary.

`copy()` is used to create another copy of the dictionary.

`fromkeys(keys, values)` takes two variables with one list of keys and one list of values/single values and returns a dictionary.


A lot of these concepts are like bread and butter while using dictionaries. You will find yourself using them quite a bit during your coding sessions so mastering them is a good idea.