# Python Built-in Functions

The Python interpreter has a number of functions and types built into it that are always available. They are listed here in alphabetical order.

## Mathematical Functions

### `abs()`
Returns the absolute value of a number.
```python
print(abs(-7.25)) # Output: 7.25
```

### `round()`
Rounds a number to a specified number of digits.
```python
print(round(5.76543, 2)) # Output: 5.77
```

### `min()` and `max()`
Returns the smallest or largest item in an iterable or of two or more arguments.
```python
print(min(5, 10, 25)) # Output: 5
print(max(5, 10, 25)) # Output: 25
```

### `sum()`
Sums the items of an iterator.
```python
print(sum([1, 2, 3, 4, 5])) # Output: 15
```

## Type Conversion

### `int()`, `float()`, `str()`
Convert values to integer, float, or string.
```python
print(int("12"))   # 12
print(float("12")) # 12.0
print(str(12))     # "12"
```

### `list()`, `tuple()`, `set()`, `dict()`
Constructors for creating collections.
```python
print(list((1, 2))) # [1, 2]
```

## Iterables and Iterators

### `len()`
Returns the length (the number of items) of an object.
```python
print(len("Hello")) # Output: 5
```

### `range()`
Returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and stops before a specified number.
```python
print(list(range(5))) # Output: [0, 1, 2, 3, 4]
```

### `enumerate()`
Takes a collection (e.g. a tuple) and returns it as an enumerate object.
```python
x = ('apple', 'banana', 'cherry')
y = enumerate(x)
print(list(y)) # Output: [(0, 'apple'), (1, 'banana'), (2, 'cherry')]
```

### `zip()`
Returns an iterator, from two or more iterables, where the first item in each iterator is paired together, and then the second item in each iterator are paired together etc.
```python
a = ("John", "Charles", "Mike")
b = ("Jenny", "Christy", "Monica")
x = zip(a, b)
print(list(x)) # Output: [('John', 'Jenny'), ('Charles', 'Christy'), ('Mike', 'Monica')]
```

### `sorted()`
Returns a sorted list of the specified iterable object.
```python
a = (1, 11, 2)
x = sorted(a)
print(x) # Output: [1, 2, 11]
```

## Input/Output

### `print()`
Prints to the standard output device.
```python
print("Hello", "World", sep="-") # Output: Hello-World
```

### `input()`
Allow user input.
```python
# x = input('Enter your name:')
```

### `open()`
Opens a file and returns a file object.
```python
# f = open("demofile.txt", "r")
```

## Object Introspection

### `type()`
Returns the type of an object.
```python
print(type(5)) # Output: <class 'int'>
```

### `id()`
Returns the identity of an object.
```python
x = ('apple', 'banana', 'cherry')
print(id(x))
```

### `dir()`
Returns a list of the specified object's properties and methods.
```python
class Person:
  name = "John"
  age = 36
  country = "Norway"

print(dir(Person))
```

### `help()`
Executes the built-in help system.
```python
# help(print)
```

## Dynamic Execution

### `eval()`
Evaluates and executes an expression.
```python
x = 'print(55)'
eval(x) # Output: 55
```

### `exec()`
Executes the specified code (or object).
```python
x = 'name = "John"\nprint(name)'
exec(x) # Output: John
```

[[programming/python/python]]