namedtuple¶

A namedtuple is a tuple subclass with named fields. It combines the immutability of tuples with the readability of classes.

Creating Named Tuples¶

```python from collections import namedtuple

Define the type¶

Scientist = namedtuple('Scientist', ['name', 'field', 'born', 'nobel'])

Create instances¶

marie = Scientist('Marie Curie', 'physics', 1867, True) einstein = Scientist(name='Albert Einstein', field='physics', born=1879, nobel=True) ```

Alternative Field Definitions¶

```python

Space-separated string¶

Point = namedtuple('Point', 'x y z')

Comma-separated string¶

RGB = namedtuple('RGB', 'red, green, blue')

List of strings¶

Person = namedtuple('Person', ['name', 'age', 'city']) ```

Accessing Fields¶

By Name (like class)¶

```python Scientist = namedtuple('Scientist', ['name', 'field', 'born', 'nobel']) s = Scientist('Marie Curie', 'physics', 1867, True)

print(s.name) # Marie Curie print(s.field) # physics print(s.born) # 1867 print(s.nobel) # True ```

By Index (like tuple)¶

python print(s[0]) # Marie Curie print(s[1]) # physics print(s[-1]) # True

Slicing¶

python print(s[:2]) # ('Marie Curie', 'physics') print(s[1:3]) # ('physics', 1867)

Immutability¶

Named tuples are immutable like regular tuples:

```python s = Scientist('Marie Curie', 'physics', 1867, True)

s.name = 'M Curie' # AttributeError: can't set attribute s[0] = 'M Curie' # TypeError: 'Scientist' object does not support item assignment ```

Creating Modified Copies¶

Use _replace() to create a new instance with some fields changed:

python s = Scientist('Marie Curie', 'physics', 1867, True) s2 = s._replace(name='M. Curie', born=1867) print(s2) # Scientist(name='M. Curie', field='physics', born=1867, nobel=True) print(s) # Original unchanged

Comparison with Regular Class¶

Regular Class (Mutable)¶

```python class Scientist: def init(self, name, field, born, nobel): self.name = name self.field = field self.born = born self.nobel = nobel

s = Scientist('Marie Curie', 'physics', 1867, True) s.name = 'M Curie' # Works! (mutable) ```

namedtuple (Immutable)¶

```python from collections import namedtuple Scientist = namedtuple('Scientist', ['name', 'field', 'born', 'nobel'])

s = Scientist('Marie Curie', 'physics', 1867, True) s.name = 'M Curie' # AttributeError (immutable) ```

Utility Methods¶

Named tuples provide special methods (prefixed with _):

_fields¶

python print(Scientist._fields) # ('name', 'field', 'born', 'nobel')

_asdict()¶

```python s = Scientist('Marie Curie', 'physics', 1867, True) print(s._asdict())

{'name': 'Marie Curie', 'field': 'physics', 'born': 1867, 'nobel': True}¶

```

_make(iterable)¶

python data = ['Albert Einstein', 'physics', 1879, True] einstein = Scientist._make(data) print(einstein) # Scientist(name='Albert Einstein', ...)

Default Values¶

Use defaults parameter (Python 3.7+):

```python Scientist = namedtuple('Scientist', ['name', 'field', 'born', 'nobel'], defaults=[None, False])

'born' defaults to None, 'nobel' defaults to False¶

s = Scientist('Marie Curie', 'physics') print(s) # Scientist(name='Marie Curie', field='physics', born=None, nobel=False) ```

Use Cases¶

Function Return Values¶

```python def get_user_info(user_id): UserInfo = namedtuple('UserInfo', ['name', 'email', 'active']) return UserInfo('Alice', 'alice@example.com', True)

info = get_user_info(123) print(info.name) # Alice (more readable than info[0]) ```

Database Records¶

python Row = namedtuple('Row', ['id', 'name', 'price']) products = [ Row(1, 'Apple', 1.50), Row(2, 'Banana', 0.75), ] for p in products: print(f"{p.name}: ${p.price}")

Coordinates and Points¶

python Point = namedtuple('Point', ['x', 'y']) p1 = Point(3, 4) p2 = Point(0, 0) distance = ((p1.x - p2.x)**2 + (p1.y - p2.y)**2)**0.5

namedtuple vs typing.NamedTuple¶

For type hints, use typing.NamedTuple:

```python from typing import NamedTuple

class Scientist(NamedTuple): name: str field: str born: int nobel: bool = False # Default value

s = Scientist('Marie Curie', 'physics', 1867) print(s.nobel) # False ```

Summary¶

Use namedtuple when:

• You need readable field names
• Immutability is desired
• Memory efficiency matters
• Simple data container without methods

Exercises¶

Exercise 1. Define a Color namedtuple with fields name, hex_code, and rgb (a tuple of three ints). Create a list of at least three colors and write a function find_by_name that takes the list and a color name string and returns the matching Color or None. For example, find_by_name(colors, "red") should return the red Color instance.

Exercise 2. Write a function csv_to_namedtuples that takes a CSV-formatted string (with a header row) and returns a list of namedtuples, where the namedtuple type is created dynamically from the header. For example, given "name,age\nAlice,30\nBob,25", it should return a list of Row(name='Alice', age='30') and Row(name='Bob', age='25').

Exercise 3. Define a Point namedtuple with fields x and y. Write a function translate that takes a Point and two offsets dx and dy, and returns a new Point shifted by those offsets using _replace(). Then write a function distance that takes two Point instances and returns the Euclidean distance between them.