The setdefault() method returns the value of a specified key. If the key does not exist, the key is inserted with the default value parameter. Usage:
```python
student = {
    "name": "John",
    "year": 2,
    "grade": 95
}

student_name = student.setdefault("name", "Joe")
print(student_name)
student_age = student.setdefault("age", 19)
print(student_age)
```
The first print statement outputs `John`, as the key "name" already exists. The second print statement outputs `19`, as there is no "age" key in the Dictionary. Additionally, the key-value pair `{"age": 19}` is added to the `student` Dictionary.

Rutgers University

Dictionaries have several useful built-in methods for altering dictionary values.
- Updating/adding to a dictionary:
A dictionary can be updated by passing in an iterable object with key:value pairs (usually another dictionary) into the update method. In the example below, the "apple" key is assigned the new value "green".
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
dict.update({"apple": "green"})
```
Additionally, if a key/value pair that doesn't exist in the dictionary is passed through the update method, it is added. This is shown below.
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
dict.update({"tangerine": "orange"})
```
-Removing values from a dictionary:
There are multiple ways of removing values from a dictionary. To remove a specific item, you can use the pop or del method by passing in the key name.
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
dict.pop("banana")
del dict["apple"]
```
If you want to remove the last item in the dictionary, you can use the popitem method. 
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
dict.popitem() #There are no parameters passed in, since popitem always removes the #last item in the dictionary.
```
You can also either remove every item from the dictionary using the clear method or delete the structure itself using the del method.
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
dict.clear() #dictionary is emptied, but still exists. It can be updated with new items if you want.
del dict #dictionary is actually deleted. Referencing it again will cause an error.
```
-Looping over a dictionary
Like removing items, there are multiple ways of iterating over dictionary items depending on if you want keys, values, or both. You will iterate via a for loop and either use the key method to return only keys, the values method to return only values, or the items method to return the full key:value pair.
```python
dict = {
	"banana": "yellow",
	"apple": "red",
	"grape": "purple"
}
for x in dict.keys():
	print(x)
for x in dict.values():
	print(x)
for x, y in dict.items():
	print(x, y)
```
Other methods that may be used include:
- copy()
- fromkeys()
- get()
- setdefault()

Dictionary Methods

Python Documentation

The clear() method removes all items from a dictionary structure.
Usage:
```python
student = {
    "name": "John Smith",
    "year": 3,
    "major": "Computer Science"
}

student.clear()
print(student)
```

The clear() method removes all items in the student dictionary. The final print statement outputs `{}`.
     

clear()

The copy() method returns a copy of the dictionary. Usage:
```python
student = {
    "name": "John Smith",
    "year": 3,
    "major": "Computer Science"
}

clone = student.copy()
print(clone)
```
The `student` dictionary is copied to `clone`. The final print statement outputs `{'name': 'John Smith', 'year': 3, 'major': 'Computer Science'}`.

copy()

fromkeys() is a class method that returns a new dictionary with the specified keys in `iterable` and the optional value `value`. If no value is provided the values will default to `None`. Usage:
```python
students = ('John', 'Joe', 'Jill')
grade = 100

student_grades = dict.fromkeys(students, grade)
print(student_grades)
```
The final print statement outputs `{'John': 100, 'Joe': 100, 'Jill': 100}`.

fromkeys(iterable[, value])

The get() method returns the value of a specified key. If the key does not exist, get() returns the optional default value. Usage:
```python
student = {
    "name": "John",
    "year": 2,
    "grade": 95
}

student_name = student.get("name")
print(student_name)
student_age = student.get("age", 19)
print(student_age)
```
The first print statement outputs `John`. The second print statement outputs `19`, as there is no age key in the Dictionary.

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