1. Inputs, Output, Strings and Help

Basic Operations with Python

Let's learn from examples:
>>> print(5,6,7)
5 6 7
​
>>> print('LOVE', 30, 82.2)
LOVE 30 82.2
​
>>> print('LOVE', 30, 82.2, sep=',')
'LOVE', 30, 82.2
​
>>> print('LOVE', 30, 82.2, sep=',', end='!!\n')
'LOVE', 30, 82.2!!
Let's play with the Input function a little bit. input() -> str
>>> beautiful_number = input()
6
​
>>> type(beautiful_number)
<class 'str'>
​
>>> beautiful_number = int(input())
6
>>> type(beautiful_number)
<class 'int'>
>>> for i in "python":
...     print(i)
...
p
y
t
h
o
n
​
​
>>> for i in "python":
...     print(i, end=":")
...
p:y:t:h:o:n:
Strings
Strings in Python are immutable.
>>> a = "hello"
​
>>> a + " dear"
'hello dear'
​
>>> a
'hello'
String Slicing
>>> a.upper()
'HELLO'
​
>>> len(a)
5
​
>>> a[0]
'h'
​
>>> a[-1]
'o'
​
>>> a[::]   # String slicing
'hello'
​
>>> a[::-1]
'olleh'
​
>>> a.find('l')
2
​
>>> a[1:3]
'el'
​
>>> a[1:]
'ello'
String Formatting
Example 1: Simple example of string format
>>> name  = "Bablu Kumar"
​
>>> number = len(name) * 3
​
>>> print("Hello {}, your lucky number is {}.".format(name, number))
Hello Bablu Kumar, your lucky number is 33.
​
​
>>> print("Hello {n}, your lucky number is {num}".format(n=name, num=len(name) * 3))
Hello Bablu Kumar, your lucky number is 33
Example 2: Showing only two numbers after the decimal.
.2f this means we're going to format a float number and that there should be two digits after the decimal dot.
>>> price = 7.5
>>> with_tax = price * 1.09
>>> print(price, with_tax)
7.5 8.175
>>> 
>>> print("Base Price: ${:.2f}, With Tax: ${:.2f}".format(price, with_tax))
Base Price: $7.50, With Tax: $8.18
Example 3:
:>3: we're using the greater than operator to align text to the right so that the output is neatly aligned.
In the first expression we're saying we want the numbers to be aligned to the right for a total of three spaces.
:>6.2f: In the second expression we're saying we want the number to always have exactly two decimal places and we want to align it to the right at six spaces.
>>> def to_celsius(x):
	return (x-32)*5/9
​
>>> for x in range(0, 101, 10):
	print("{:>3} F | {:>6.2f} C".format(x, to_celsius(x)))
​
	
  0 F | -17.78 C
 10 F | -12.22 C
 20 F |  -6.67 C
 30 F |  -1.11 C
 40 F |   4.44 C
 50 F |  10.00 C
 60 F |  15.56 C
 70 F |  21.11 C
 80 F |  26.67 C
 90 F |  32.22 C
100 F |  37.78 C
Notice the difference between :>3 and :<3 in the string formatting.
>>> def to_celsius(x):
	return (x-32)*5/9
	
>>> for x in range(0, 101, 10):
	print("{:<3} F | {:>4.2f} C".format(x, to_celsius(x)))
​
	
0   F | -17.78 C
10  F | -12.22 C
20  F | -6.67 C
30  F | -1.11 C
40  F | 4.44 C
50  F | 10.00 C
60  F | 15.56 C
70  F | 21.11 C
80  F | 26.67 C
90  F | 32.22 C
100 F | 37.78 C
F-String
### Example 1
​
>>> name = "BK"
>>> age = 34
>>> print(f"My name is {name}. I am {age} years old.")
My name is BK. I am 34 years old.
​
### Example 2
​
>>> print(f"The \"comedian\" is {name}, aged {age}.")
'The "comedian" is BK, aged 34.'
​
### Example 3
​
>>> print(f"The \"comedian\" is {name}, aged {age:.2f}")
The "comedian" is BK, aged 34.00
​
​
### Example 4
​
>>> comedian = {'name': 'Eric Idle', 'age': 74}
>>> print(f"My name is {comedian['name']}. My age is {comedian['age']}")
My name is Eric Idle. My age is 74
Cheat Sheet
Expr
Meaning
Example
{:d}
integer value
'{:d}'.format(10.5) → '10'
{:.2f}
floating point with that many decimals
'{:.2f}'.format(0.5) → '0.50'
{:.2s}
string with that many characters
'{:.2s}'.format('Python') → 'Py'
{:<6s}
string aligned to the left that many spaces
'{:<6s}'.format('Py') → 'Py    '
{:>6s}
string aligned to the right that many spaces
'{:>6s}'.format('Py') → '    Py'
{:^6s}
string centered in that many spaces
'{:^6s}'.format('Py') → '  Py '
String Methods
s.lower(), s.upper() -- returns the lowercase or uppercase version of the string
s.strip() -- returns a string with whitespace removed from the start and end
s.isalpha()/s.isdigit()/s.isspace()... -- tests if all the string chars are in the various character classes
s.startswith('other'), s.endswith('other') -- tests if the string starts or ends with the given other string
s.find('other') -- searches for the given other string (not a regular expression) within s, and returns the first index where it begins or -1 if not found
s.replace('old', 'new') -- returns a string where all occurrences of 'old' have been replaced by 'new'
s.split('delim') -- returns a list of substrings separated by the given delimiter. The delimiter is not a regular expression, it's just text. 'aaa,bbb,ccc'.split(',') -> ['aaa', 'bbb', 'ccc']. As a convenient special case s.split() (with no arguments) splits on all whitespace chars.
s.join(list) -- opposite of split(), joins the elements in the given list together using the string as the delimiter. e.g. '---'.join(['aaa', 'bbb', 'ccc']) -> aaa---bbb---ccc
Help for Python
dir() and help()
Use search engines
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2. Lists, Sorting, and Tuples and Dictionaries

Last updated 6 months ago

Expr	Meaning	Example
{:d}	integer value	'{:d}'.format(10.5) → '10'
{:.2f}	floating point with that many decimals	'{:.2f}'.format(0.5) → '0.50'
{:.2s}	string with that many characters	'{:.2s}'.format('Python') → 'Py'
{:<6s}	string aligned to the left that many spaces	'{:<6s}'.format('Py') → 'Py '
{:>6s}	string aligned to the right that many spaces	'{:>6s}'.format('Py') → ' Py'
{:^6s}	string centered in that many spaces	'{:^6s}'.format('Py') → ' Py '