Python numbers, strings, list types (Python learning memo ①)

Python type

Numerical value

point

• Division (/) always returns a float
• Use the // operator if you want to perform a devaluation division to get an int type
• Use % if you want to get the remainder
• If the types to be operated on are mixed, the integer is converted to a floating point number.
• In interactive mode, the last displayed expression is assigned to the variable " _ ", so it is easy to use with a calculator.
• In addition to integer type and floating point type, Python supports decimal numbers (Decimal) and rational numbers (Fraction).
• Complex numbers are also supported, using the suffix j or J to represent imaginary parts, such as 3 + 5j.

#addition
>>> 2+2              
4
      
#Subtraction and multiplication
>>> 50 - 5 * 6        
20                   
>>> (50 - 5) *6      
270

#division
>>> 17 / 3       
5.666666666666667
>>> 17 // 3      
5                
>>> 17 % 3       
2

#Get both quotient and remainder
>>> divmod(17, 3)
(5, 2)

#radix
# 0b:Binary
# 0o:Octal
# 0x:Hexadecimal
>>> 0b10
2
>>> 0o10
8
>>> 0x10
16

#Exponentiation
>>> 5 ** 2
25
>>> 5 ** 3
125

#Use interactive mode as a calculator
>>> _ + 1
126

String type

point

• Quotation marks can be either single quotes or double quotes and are indistinguishable
• Quarting characters can be escaped with \
• Use the raq string if you don't want the string prefixed with \ to be interpreted as a special character
• Multi-line strings can be represented by triple quotes
• End-of-line characters are automatically included in the string, but if you don't want to start a newline, put \ at the end of the line to escape
• Strings can be combined with the + operator and can be repeated with the *
• If string literals are consecutive, they are automatically concatenated.
• Character strings can be indexed
• Index is a number that points between letters, with the first letter being the 0th (starting with 0)
• Strings can be sliced
• An error will occur if you specify a value outside the range in the index.
• Slicing does not cause an error even if specified outside the range
• Since the python string is immutable, you cannot modify the character using the index (create a new string if you want to)
• The len function returns the length of the string

#In the path name/Can be used, so the following is unnecessary
# raw name (Prefix the string with r)
>>> print('C:\some\name')
C:\some
ame
>>> print(r'C:\some\name')
C:\some\name

#Multiple lines
print("""\
    Usage: thingy [OPTIONS]
        -h Display this usage message
        -H hostname   
""")
#output
Usage: thingy [OPTIONS]
        -h Display this usage message
        -H hostname

#Repeat and concatenate strings
>>> 3 * "un" + "ium" 
'unununium'

#Automatic concatenation of string literals(Cannot be used with variables)
>>> 'Py' 'thon' 
'Python'

# index
>>> word[0]
'P'
>>> word[-1] 
'n'

# slice
>>> word[:3] 
'Pyt'
>>> word[3:] 
'hon'

# len
>>> len(word) 
6

list

point

• Basically put the same type
• Like strings, you can use indexes and slicing
• Slicing always returns a new list containing the requested elements
• Lists are mutable, unlike strings, so they can be changed
• Add an element to the end with .append
• Substitution to slicing is also possible
• The len function can also be used for lists
• Lists can be nested

#list
>>> letters = ['a', 'b', 'c', 'd', 'e', 'f']
# index
>>> letters[1] 
'b'

# slicing
>>> letters[3:] 
['d', 'e', 'f']

# append
>>> letters.append('g') 
>>> letters
['a', 'b', 'c', 'd', 'e', 'f', 'g']

#Substitution to slicing
>>> letters[3:5] = ['D', 'E'] 
>>> letters
['a', 'b', 'c', 'D', 'E', 'f', 'g']

# len
>>> len(letters)
7

#Nested list
>>> array = [['a', 'b', 'c'], [1, 2, 3]] 

Find the Fibonacci sequence

#Fibonacci series
#Multiple assignment is possible in this way
a, b = 0, 1

while b < 10:
    print(b)
    a, b = b, a+b

About the print function

• Multiple values can be specified as arguments
• The keyword argument end can be used to suppress line breaks at the end of the output or change the end of the output to another string.
• The keyword argument sep can be used to change the string that separates the output values.

name = 'Kawausomando'
#Specify multiple values(Space is given between)
print('My name is', name)
#output: My name is Kawausomando

#end keyword
print(name, end=' is my name')
#output: Kawausomando is my name

#sep keyword
print(1, 2, 3, sep=' and ')
#output: 1 and 2 and 3