Built-in functions¶
There are a set of built-in functions that are a part of any Python installation, i.e., they can be used and recognised in any Python code. The built-in functions do not have to be imported.
We will describe a few common functions here, but there are many more, that are described at https://docs.python.org/3/library/functions.html.
abs¶
The abs() function will return the
absolute value of a real or complex number, e.g.:
print(abs(-2.3))
2.3
print(abs(4.5 + 1.2j))
4.65725240888
dict¶
The dict() function is used to create a
new dictionary, e.g.:
d = dict(value1=1, value2=2)
print(d)
{'value1': 1, 'value2': 2}
enumerate¶
The enumerate() function is used
when iterating over an object such as a list or array. For each iteration, it returns a tuple
containing an index, and the value of the element at that index, e.g.:
x = [7.4, 1.0, 5.6, 13.2]
y = ["a", "b", "c", "d"]
for i, x_val in enumerate(x):
print(x_val, y[i])
float¶
The float() function creates a floating point number object from a number or a string, e.g.:
num = float("4.5") # convert a string containing 4.5 into a float representing 4.5
int¶
The int() function creates an integer object
from a number or a string, e.g.:
num = int("3") # convert a string containing 3 into an int representing 3
input¶
The input() function allows you to get
user input from the keyboard, e.g.:
name = input("What is your name? ")
isinstance¶
The isinstance() function allows
you to check whether a variable is of a particular class (or subclass of a given class), e.g.,:
x = 2
# check x is an integer
test = isinstance(x, int)
print(test)
True
len¶
The len() function returns the length of an
object, such as a list, if this is meaningful for that object, e.g.,:
x = [4, 9, 2, 6]
len(x)
4
list¶
The list() function (actually a "mutable
sequence" rather than a function) is used
to create a new list, e.g.,:
l = list((1, 2, 3))
print(l)
[1, 2, 3]
max¶
The max() function returns the largest
value in a list of values, or the largest value from a set of arguments, e.g.:
print(max([5, 7, 2, 1, 7]))
7
print(max(5, 7, 2, 1, 7))
7
min¶
The min() function returns the smallest
value in a list of values, or the smallest value from a set of arguments, e.g.:
print(min([5, 7, 2, 1, 7]))
1
print(min(5, 7, 2, 1, 7))
1
print¶
The print() function allows you
to print text to the screen or a file, e.g.:
print("Hello")
Hello
Note
print just prints text to the screen (or to a file if
specified). It does not return that text to a variable.
range¶
The range() function returns a
sequence of values that can be iterated through. It can be used to create a list of integer values
starting at zero and going up to one less than the supplied value, e.g.,:
idxs = list(range(10))
print(idx)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
and is useful for iterating over a range of indices in a for-loop, e.g.:
x = [6.6, 7.4, 3.4, 2.1]
for i in range(len(x)):
print(x[i])
str¶
The str() function returns a string
representation of an object, e.g.:
numstr = str(3) # get a string version of the integer number object 3
sum¶
The sum() function will sum the items
within a list (or other iterable), e.g.:
sum([2, 3, 4, 5, 6])
20
type¶
The type() function return the type of a
variable.
type("Hello")
str
Keywords¶
Along with the built-in functions, there are a set of reserved keywords in Python that have a specific meaning and cannot be used for variable or function names.
A list of the current keywords can be found by importing the [keyword] module and printing the
kwlist value, e.g.:
import keyword
for i in range(len(keyword.kwlist) // 5):
print("\t".join(keyword.kwlist[(i * 5):(i * 5 + 5)]))
False None True and as
assert async await break class
continue def del elif else
except finally for from global
if import in is lambda
nonlocal not or pass raise
return try while with yield
Many of these keywords will be defined in other tutorials, but a good resource defining them all can be found here.