# How To Use Python3 To Match Against Multiple Criteria

Using Python3 to match against multiple criteria is relatively simple. In this article, I will tell you how to implement it using 2 methods. One way is to use the python `all` function, the other way is to use the python `itertools` library.

## 1. How To Use Python3 all Function To Match Against Multiple Criteria?

1. All you need to do is create a list of the criteria you would like to match against and then use the `all` function to check if all criteria are met.
2. Let’s say you have a list of people and you want to find all people whose age is greater than 18, who are not married, and who have a salary greater than \$35,000.
3. You can use the following code to match against those criteria.
```# Create a list of people
people = [
{ 'name': 'Alice', 'age': 21, 'married': False, 'salary': 40000 },
{ 'name': 'Bob', 'age': 27, 'married': True, 'salary': 30000 },
{ 'name': 'Carol', 'age': 33, 'married': False, 'salary': 45000 }
]

# Create a list of criteria
criteria = [
lambda person: person['age'] > 18,
lambda person: not person['married'],
lambda person: person['salary'] > 35000
]

# Use the all function to check if all criteria are met
matching_people = [person for person in people if all(criterion(person) for criterion in criteria)]

# Print matching people
for person in matching_people:
print(person['name'])

# Output: Alice, Carol```
4. The code above will print out the names of all people in the list who match the given criteria. As you can see, it is relatively straightforward to use Python3 to match against multiple criteria.

### 1.1 Python all function’s explanation.

1. If you are not familiar with the python `all` function, you can see the below explanation.
2. The all() function in Python returns True if all elements in an iterable are true, or if the iterable is empty.
3. It returns False if any element in the iterable is false.
4. The all() function takes an iterable object (such as a list, dictionary, set, tuple, string, etc.) as an argument and returns True if all elements in the iterable are true, or if the iterable is empty.

## 2. How To Use Python3 itertools Library To Match Against Multiple Criteria?

1. Python3 has a powerful set of tools to match against multiple criteria. You can easily filter out certain criteria with the built-in functions like `filter()` and `map()`.
2. You can also use the `itertools` library to chain multiple criteria together.
3. Here is an example of how to use `filter()` and `map()` to match against multiple criteria.

```from itertools import chain

# Define the criteria
criteria = [
lambda x: x > 3,
lambda x: x % 2 == 0
]

# Use filter() to filter out elements that don't match the criteria
filtered_list = list(
filter(lambda x: all(c(x) for c in criteria), my_list)
)

# Use map() to apply a function to each element of the filtered list
mapped_list = list(
map(lambda x: x * 2, filtered_list)
)```
4. You can also use the `itertools.chain()` function to chain multiple criteria together. This is useful when you want to apply multiple conditions to the same list.
```from itertools import chain

# Define the criteria
criteria = [
lambda x: x > 3,
lambda x: x % 2 == 0
]

# Chain the criteria together
chained_criteria = chain(*criteria)

# Use filter() to filter out elements that don't match the chained criteria
filtered_list = list(
filter(lambda x: all(c(x) for c in chained_criteria), my_list)
)```
5. By using the built-in functions and the `itertools` library, you can easily match against multiple criteria in Python3.

### 2.1 Python itertools module filter function’s explanation.

1. The filter() function from the itertools module is a built-in function that filters out elements from a sequence based on a specified rule.
2. It takes a function and a sequence, and applies the function to the sequence one element at a time.
3. If the function returns True, the element is kept, otherwise, it is removed.

### 2.2 Python itertools module map function’s explanation.

1. The map() function from the itertools module is a built-in function that applies a function to each element of a sequence (which may be one or more parameters).
2. Each time map() is called, and it will return an iterator containing the results of the function.

### 2.3 Python itertools module chain function’s explanation.

1. The chain() function from the itertools module is a built-in function that returns a sequence of values from multiple sequences of iterables.
2. It accepts one or more iterables and returns them as a single iterable object.
3. This allows for the efficient and easy combining of multiple iterables into a single sequence.

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