Every value in Python has a datatype. Since everything is an object in Python programming, data types are actually classes and variables are instance (object) of these classes.
There are various data types in Python. Some of the important types are listed below.
Integers, floating point numbers and complex numbers falls under Python numbers category. They are defined as int, float and complex class in Python.
int
float
complex
We can use the type() function to know which class a variable or a value belongs to and the isinstance() function to check if an object belongs to a particular class.
type()
isinstance()
a = 5 print(a, "is of type", type(a)) a = 2.0 print(a, "is of type", type(a)) a = 1+2j print(a, "is complex number?", isinstance(1+2j,complex))
Integers can be of any length, it is only limited by the memory available.
A floating point number is accurate up to 15 decimal places. Integer and floating points are separated by decimal points. 1 is integer, 1.0 is floating point number.
1
1.0
Complex numbers are written in the form, x + yj, where x is the real part and y is the imaginary part. Here are some examples.
x + yj
>>> a = 1234567890123456789 >>> a 1234567890123456789 >>> b = 0.1234567890123456789 >>> b 0.12345678901234568 >>> c = 1+2j >>> c (1+2j)
Notice that the float variable b got truncated.
List is an ordered sequence of items. It is one of the most used datatype in Python and is very flexible. All the items in a list do not need to be of the same type.
Declaring a list is pretty straight forward. Items separated by commas are enclosed within brackets [ ].
>>> a = [1, 2.2, 'python']
We can use the slicing operator [ ] to extract an item or a range of items from a list. Index starts form 0 in Python.
a = [5,10,15,20,25,30,35,40] # a[2] = 15 print("a[2] = ", a[2]) # a[0:3] = [5, 10, 15] print("a[0:3] = ", a[0:3]) # a[5:] = [30, 35, 40] print("a[5:] = ", a[5:])
Lists are mutable, meaning, value of elements of a list can be altered.
>>> a = [1,2,3] >>> a[2]=4 >>> a [1, 2, 4]
Tuple is an ordered sequence of items same as list.The only difference is that tuples are immutable. Tuples once created cannot be modified.
Tuples are used to write-protect data and are usually faster than list as it cannot change dynamically.
It is defined within parentheses () where items are separated by commas.
>>> t = (5,'program', 1+3j)
We can use the slicing operator [] to extract items but we cannot change its value.
t = (5,'program', 1+3j) # t[1] = 'program' print("t[1] = ", t[1]) # t[0:3] = (5, 'program', (1+3j)) print("t[0:3] = ", t[0:3]) # Generates error # Tuples are immutable t[0] = 10
String is sequence of Unicode characters. We can use single quotes or double quotes to represent strings. Multi-line strings can be denoted using triple quotes, ''' or """.
'''
"""
>>> s = "This is a string" >>> s = '''a multiline
Like list and tuple, slicing operator [ ] can be used with string. Strings are immutable.
s = 'Hello world!' # s[4] = 'o' print("s[4] = ", s[4]) # s[6:11] = 'world' print("s[6:11] = ", s[6:11]) # Generates error # Strings are immutable in Python s[5] ='d'
Set is an unordered collection of unique items. Set is defined by values separated by comma inside braces { }. Items in a set are not ordered.
a = {5,2,3,1,4} # printing set variable print("a = ", a) # data type of variable a print(type(a))
We can perform set operations like union, intersection on two sets. Set have unique values. They eliminate duplicates.
>>> a = {1,2,2,3,3,3} >>> a {1, 2, 3}
Since, set are unordered collection, indexing has no meaning. Hence the slicing operator [] does not work.
>>> a = {1,2,3} >>> a[1] Traceback (most recent call last): File "<string>", line 301, in runcode File "<interactive input>", line 1, in <module> TypeError: 'set' object does not support indexing
Dictionary is an unordered collection of key-value pairs.
It is generally used when we have a huge amount of data. Dictionaries are optimized for retrieving data. We must know the key to retrieve the value.
In Python, dictionaries are defined within braces {} with each item being a pair in the form key:value. Key and value can be of any type.
key:value
>>> d = {1:'value','key':2} >>> type(d) <class 'dict'>
We use key to retrieve the respective value. But not the other way around.
d = {1:'value','key':2} print(type(d)) print("d[1] = ", d[1]); print("d['key'] = ", d['key']); # Generates error print("d[2] = ", d[2]);
We can convert between different data types by using different type conversion functions like int(), float(), str() etc.
>>> float(5) 5.0
Conversion from float to int will truncate the value (make it closer to zero).
>>> int(10.6) 10 >>> int(-10.6) -10
Conversion to and from string must contain compatible values.
>>> float('2.5') 2.5 >>> str(25) '25' >>> int('1p') Traceback (most recent call last): File "<string>", line 301, in runcode File "<interactive input>", line 1, in <module> ValueError: invalid literal for int() with base 10: '1p'
We can even convert one sequence to another.
>>> set([1,2,3]) {1, 2, 3} >>> tuple({5,6,7}) (5, 6, 7) >>> list('hello') ['h', 'e', 'l', 'l', 'o']
To convert to dictionary, each element must be a pair
>>> dict([[1,2],[3,4]]) {1: 2, 3: 4} >>> dict([(3,26),(4,44)]) {3: 26, 4: 44}