8.1. Builtin Functions

8.1.1. Power - pow()

• pow() - Raise number to the power of exponential (the same as **)

>>> pow(2, 4)
16
>>>
>>> pow(16, 1/2)
4.0

Builtin function pow() raises number to the n-th power. Note, that arithmetic operator ** also raises number to the power:

>>> pow(10, 2)
100
>>>
>>> pow(2, -1)
0.5

>>> pow(1.337, 3)
2.389979753
>>>
>>> pow(4, 0.5)
2.0
>>>
>>> pow(2, 0.5)
1.4142135623730951

Builtin function pow() can be used to calculate roots of a number:

>>> pow(4, 1/2)
2.0
>>>
>>> pow(2, 1/2)
1.4142135623730951
>>>
>>> pow(27, 1/3)
3.0

>>> pow(4, -1/2)
0.5
>>>
>>> pow(2, -1/2)
0.7071067811865476
>>>
>>> pow(27, -1/3)
0.33333333333333337

>>> pow(-2, -1)
-0.5
>>>
>>> pow(-4, -1)
-0.25

Builtin function pow() can return complex numbers. Note that Python has special complex() numeric type.

>>> pow(-2, -1/2)
(4.329780281177467e-17-0.7071067811865476j)
>>>
>>> pow(-2, 1/2)
(8.659560562354934e-17+1.4142135623730951j)
>>>
>>> pow(-4, -1/2)
(3.061616997868383e-17-0.5j)
>>>
>>> pow(-4, 1/2)
(1.2246467991473532e-16+2j)

8.1.2. Slice Function

• Every n-th element

• sequence[start:stop:step]

• start defaults to 0

• stop defaults to len(sequence)

• step defaults to 1

>>> text = 'We choose to go to the Moon!'
>>>
>>> q = slice(23, 27)
>>> text[q]
'Moon'
>>>
>>> q = slice(None, 9)
>>> text[q]
'We choose'
>>>
>>> q = slice(23, None)
>>> text[q]
'Moon!'
>>>
>>> q = slice(23, None, 2)
>>> text[q]
'Mo!'
>>>
>>> q = slice(None, None, 2)
>>> text[q]
'W hoet ot h on'

8.1.3. abs() - Absolute value

• abs() - Absolute value

>>> abs(1)
1
>>>
>>> abs(-1)
1

>>> abs(1.2)
1.2
>>>
>>> abs(-1.2)
1.2

>>> abs(+0)
0
>>> abs(-0)
0

8.1.4. range()

• Tworzy iterator, który zwraca liczby w sekwencji.

for liczba in range(0, 5):
    print(liczba)
# 0
# 1
# 2
# 3
# 4

for liczba in range(0, 5, 2):
    print(liczba)
# 0
# 2
# 4

numbers_generator = range(0, 5)

print(numbers_generator)
# range(0, 5)

numbers_generator = range(0, 5)
numbers = list(numbers_generator)

print(numbers)
# [0, 1, 2, 3, 4]

8.1.5. type()

type(1)                 # <class 'int'>
type(1.2)               # <class 'float'>
type('hello')           # <class 'str'>

type(True)              # <class 'bool'>
type(False)             # <class 'bool'>
type(None)              # <class 'NoneType'>

type([1, 2])            # <class 'list'>
type((1, 2))            # <class 'tuple'>
type({1, 2})            # <class 'set'>
type({1: 2})            # <class 'dict'>

type(1) == int          # True
type(1.2) == float      # True

type(True) == bool      # True
type(False) == bool     # True

type(True) == int       # False
type(False) == int      # False

type(None) == int       # False
type(None) == bool      # False
type(None) == None      # False

8.1.6. isinstance()

• Sprawdza czy dany obiekt jest instancją danej klasy

• Jeżeli jest więcej niż jeden typ to musi być tuple a nie list lub set

isinstance(10, int)             # True
isinstance(10, float)           # False
isinstance(10, (int, float))    # True

isinstance(True, float)         # False
isinstance(True, int)           # True
isinstance(True, bool)          # True

isinstance(False, float)        # False
isinstance(False, int)          # True
isinstance(False, bool)         # True

isinstance(None, int)           # False
isinstance(None, bool)          # False
isinstance(None, float)         # False

8.1.7. issubclass()

8.1.8. any()

DATA = [1, 2, 'three', 4]

if any(isinstance(x, str) for x in DATA):
    print(True)
else:
    print(False)

# True

8.1.9. all()

DATA = [1, 2, 'three', 4]

if all(isinstance(x, int) for x in DATA):
    print(True)
else:
    print(False)

# False

8.1.10. sum()

sum(x for x in range(0, 100))
# 4950

8.1.11. len()

DATA = [1, 2, 3]

len(DATA)
# 3

8.1.12. slice()

• slice() arguments must be int (positive, negative or zero)

• start (inclusive), default: 0

• stop (exclusive), default: len(...)

• step, default: 1

data = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
get = slice(1)

data[get]
# ['a']

data = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
get = slice(2, 7)

data[get]
# ['c', 'd', 'e', 'f', 'g']

data = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
get = slice(2, 7, 2)

data[get]
# ['c', 'e', 'g']

data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

get = slice(1)
data[get]
# [0]

get = slice(2, 7)
data[get]
# [2, 3, 4, 5, 6]

get = slice(2, 7, 2)
data[get]
# [2, 4, 6]

text = 'We choose to go to the Moon!'
get = slice(23, 28)

text[get]
# 'Moon!'

8.1.13. bin()

• Konwertuje liczbę na binarną

• Nie stosuje kodu uzupełnień do dwóch

0b101111    # 47

bin(3)      # '0b11'
bin(-3)     # '-0b11'

8.1.14. hex()

• Konwertuje liczbę na heksadecymalną

• Konwersja kolorów w HTML

• Shellcode

hex(99)  # '0x63'

8.1.15. oct()

• Konwertuje liczbę na oktalną

• Przydatne do uprawnień w systemie operacyjnym

oct(33261)  # '0o100755'

8.1.16. ord()

Zwraca kod ASCII jedno-znakowego stringa.

ord('a')  # 97

8.1.17. chr()

Z pozycji w tablicy ASCII konwertuje kod na znak Unicode.

chr(97)  # 'a'

8.1.18. eval()

eval('name="José Jiménez"; print(name)')
# José Jiménez

8.1.19. Other builtin functions

Table 8.14. Most used Built-in functions

Name	Description
abs()	Return the absolute value of the argument.
all()	Return True if bool(x) is True for all values x in the iterable.
any()	Return True if bool(x) is True for any x in the iterable.
ascii()	Return an ASCII-only representation of an object.
bin()	Return the binary representation of an integer.
bool()	bool(x) -> bool
bytearray()	bytearray(iterable_of_ints) -> bytearray
bytes()	bytes(iterable_of_ints) -> bytes
callable()	Return whether the object is callable (i.e., some kind of function).
chr()	Return a Unicode string of one character with ordinal i; 0 <= i <= 0x10ffff.
classmethod()	classmethod(function) -> method
compile()	Compile source into a code object that can be executed by exec() or eval().
complex()	Create a complex number from a real part and an optional imaginary part.
delattr()	Deletes the named attribute from the given object.
dict()	dict() -> new empty dictionary
dir()	dir([object]) -> list of strings
divmod()	Return the tuple (x//y, x%y). Invariant: div*y + mod == x.
enumerate()	Return an enumerate object.
eval()	Evaluate the given source in the context of globals and locals.
exec()	Execute the given source in the context of globals and locals.
filter()	filter(function or None, iterable) --> filter object
float()	Convert a string or number to a floating point number, if possible.
format()	Return value.__format__(format_spec)
frozenset()	frozenset() -> empty frozenset object
getattr()	getattr(object, name[, default]) -> value
globals()	Return the dictionary containing the current scope's global variables.
hasattr()	Return whether the object has an attribute with the given name.
hash()	Return the hash value for the given object.
help()	Define the builtin 'help'.
hex()	Return the hexadecimal representation of an integer.
id()	Return the identity of an object.
input()	Read a string from standard input. The trailing newline is stripped.
int()	int([x]) -> integer
isinstance()	Return whether an object is an instance of a class or of a subclass thereof.
issubclass()	Return whether 'cls' is a derived from another class or is the same class.
iter()	iter(iterable) -> iterator
len()	Return the number of items in a container.
list()	Built-in mutable sequence.
locals()	Return a dictionary containing the current scope's local variables.
map()	map(func, *iterables) --> map object
max()	max(iterable, *[, default=obj, key=func]) -> value
memoryview()	Create a new memoryview object which references the given object.
min()	min(iterable, *[, default=obj, key=func]) -> value
next()	next(iterator[, default])
object()	The most base type
oct()	Return the octal representation of an integer.
open()	Open file and return a stream. Raise OSError upon failure.
ord()	Return the Unicode code point for a one-character string.
pow()	Equivalent to x**y (with two arguments) or x**y % z (with three arguments)
print()	print(value, ..., sep=' ', end='n', file=sys.stdout, flush=False)
property()	Property attribute.
range()	range(stop) -> range object
repr()	Return the canonical string representation of the object.
reversed()	Return a reverse iterator over the values of the given sequence.
round()	Round a number to a given precision in decimal digits.
set()	set() -> new empty set object
setattr()	Sets the named attribute on the given object to the specified value.
slice()	slice(stop)
sorted()	Return a new list containing all items from the iterable in ascending order.
staticmethod()	staticmethod(function) -> method
str()	str(object='') -> str
sum()	Return the sum of a 'start' value (default: 0) plus an iterable of numbers
super()	super() -> same as super(__class__, <first argument>)
tuple()	Built-in immutable sequence.
type()	type(object_or_name, bases, dict)
vars()	vars([object]) -> dictionary
zip()	zip(iter1 [,iter2 [...]]) --> zip object

8.1.20. Assignments

Code 8.64. Solution

"""
* Assignment: Builtin Function Average
* Complexity: easy
* Lines of code: 12 lines
* Time: 13 min

English:
    1. Separate header and rows
    2. Define dict `result: dict[str, list]`, keys are column names from header
    3. For each row, add values to proper lists in `result`
    4. Define function `mean()`, calculating mean for arbitrary number of arguments
    5. Return `None` if any argument to the function is not `float` or `int`
    6. To calculate mean use built-in functions
    7. Iterating over `result` print column name and calculated average
    8. Run doctests - all must succeed

Polish:
    1. Odseparuj nagłówek od wierszy danych
    2. Zdefiniuj słownik `result: dict[str, list]`, klucze to nazwy kolumn z nagłówka
    3. Dla każdego wiersza, dodawaj wartości do odpowiednich list w `result`
    4. Zdefiniuj funkcję `mean()`, liczącą średnią dla dowolnej ilości argumentów
    5. Zwróć `None` jeżeli którykolwiek z argumentów do funkcji nie jest `float` lub `int`
    6. Do wyliczenia średniej wykorzystaj wbudowane funkcje
    7. Iterując po `result` wypisz nazwę kolumny oraz wyliczoną średnią
    8. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> result  # doctest: +NORMALIZE_WHITESPACE
    {'sepal_length': 5.666666666666667,
     'sepal_width': 3.0500000000000003,
     'petal_length': 3.6666666666666665,
     'petal_width': 1.1500000000000001,
     'species': None}
"""

DATA = [
    ('sepal_length', 'sepal_width', 'petal_length', 'petal_width', 'species'),
    (5.8, 2.7, 5.1, 1.9, 'virginica'),
    (5.1, 3.5, 1.4, 0.2, 'setosa'),
    (5.7, 2.8, 4.1, 1.3, 'versicolor'),
    (6.3, 2.9, 5.6, 1.8, 'virginica'),
    (6.4, 3.2, 4.5, 1.5, 'versicolor'),
    (4.7, 3.2, 1.3, 0.2, 'setosa'),]

result = {}