Overview
This article provides an easier-to-understand summary of all the content in 3. An Informal Introduction to Python from the official Python v3.13 Tutorial.
In the Python interpreter, the >>> and ... prompts distinguish input from output.
1. Using Python as a Calculator
1.1. Numbers
Python can act like a calculator.
* is the multiplication operator, ** is the exponentiation operator, // is the floor division operator, and % is the remainder operator.
The order of operations is: 1st: **, 2nd: *, /, //, %, 3rd: +, -.
- You can use +, -, *, **, /, //, %, ().
- Operations are performed in the order of ** > *, /, //, % > +, -.
>>>2+3-(5*2**3/4+7//2+8%5) #In the operation 5*2**3/4, ** is calculated first -11
The data type for integers is int, and for numbers with a fractional part (like 4.0, 1.7), the data type is float. If a calculation involves both floats and ints, the result will be a float. Also, the result of a / operation is always a float, even if the result is a whole number.
- The data type for integers is int, and for numbers with a fractional part, it is float.
- The result of a / operation is always a float.
= is used to assign a value to a variable.
_ represents the most recently printed expression.
>>> weight=60 >>> height=1.6 >>> weight/height**2 #This is a BMI calculation 23.437499999999996 >>> _//3 7.0
1.2. Strings
The data type for characters is str.
They can be represented with '...' or "..."
However, when you need to include a ' or " within a string, you must escape it with a \.
To create a newline, use \n. This is only rendered when using print().
However, if you want to include \n as literal characters in a string, you can prefix the string with r to prevent its interpretation.
>>> k='First line.\nSecond line.' >>> k 'First line.\nSecond line.' >>>print(k) First line. Second line. >>>print('C:\some\name') C:\some ame >>>print(r'C:\some\name') C:\some\name
Strings also support arithmetic operations. They can also be concatenated by placing them next to each other without the + operator. However, when concatenating with a variable, the + operator is required.
>>> 5*'doble'+'cheeseburger' 'dobledobledobledobledoblecheeseburger'
You can get the nth character using []. Using a negative number starts from the right. An error will occur if the index is out of range.
Also, using [m:n] allows you to get characters from the (m+1)th to the nth position. This works even if the indices are out of range.
Using [:m] and [m:] you can get characters from the beginning to the mth position, and from the (m+1)th position to the end, respectively.
s[:i] + s[i:] is always equal to s.
len() returns the length of the string.
>>> word = 'python' 'python' >>> word[-6] 'p' >>> word[:2] 'py' >>> len(word) 6
The list is the most versatile compound data type. It is written as a list of comma-separated values between square brackets, like [m, n]. It supports methods similar to strings, as well as addition (concatenation). You can also change the elements of a list.
You can use list.append() to add an item to the end of the list.
List elements can be not only numbers but also strings or even other lists.
list[:] creates a shallow copy of the list. Use this when you want to create a new, modified list while leaving the original unchanged.
>>> primes = [2, 3, 5, 7] >>> primes [2, 3, 5, 7] >>> primes[4]=11 >>> primes [2, 3, 5, 11] >>> kprimes=primes[:] >>> kprimes.append(13) >>> primes [2, 3, 5, 11] >>> len(kprimes) 5 >>> x = [primes, kprimes] [[2, 3, 5, 11], [2, 3, 5, 11, 13]]
Reference
[1] Python Software Foundation. "3. An Informal Introduction to Python." The Python Tutorial, version 3.13, Python Software Foundation, 2024, https://docs.python.org/3.13/tutorial/introduction.html, Accessed 10 July 2025.
