-Memo # 1 for Python beginners to read "Detailed explanation of Python grammar" -Memo # 2 for Python beginners to read "Detailed Explanation of Python Grammar" -Memo # 3 for Python beginners to read "Detailed explanation of Python grammar"
is
#Returns true for the same object
>>> a = b = [1, 2, 3]
>>> a is b
True
#In this case it is a different object so the result of is is false
>>> a = [1, 2, 3]
>>> b = [1, 2, 3]
>>> a is b
False
>>> a == b
True
#The result of is is judged by the id of the object
>>> id(a)
4353816328
>>> id(b)
4353060616
>>> a = b = [1, 2, 3]
>>> id(a)
4353816392
>>> id(b)
4353816392
Conditional operator (ternary operator)
>>> x = 1
>>> 100 if x == 1 else 200
100
>>> x = 2
>>> 100 if x == 1 else 200
200
>>> x == 1 and 100 or 200 #Rewriting by and and or
200
Automatic type conversion of numerical calculation results
>>> 1 + 1.0 #integer+Floating point number
2.0 #The result is a floating point number
>>> 1 + 1j #integer+Complex number
(1+1j) #The result is a complex number
Numerical calculation method
>>> divmod(20, 6)
(3, 2) #The quotient and remainder of the division are returned as tuples. It looks convenient.
>>> pow(3, 4) # 3 **Same as 4
81
>>> pow(3, 4, 5) # 3 ** 4 %Same as 5, but faster
1
int([x, byte])
#Returns 0 with no arguments
>>> int()
0
#If you pass a floating point number, it will be rounded to 0
>>> int(10.5)
10
>>> int(-10.5)
-10
#Cardinal number can be specified when passing a character string
>>> int('100') #Decimal number when radix is omitted
100
>>> int('100', 2)
4
>>> int('100', 8)
64
>>> int('100', 10)
100
>>> int('100', 16)
256
#Convert as an integer literal, where the radix is 0
>>> int('100', 0)
100
>>> int('0b100', 0)
4
>>> int('0o100', 0)
64
>>> int('0x100', 0)
256
#Converts any character that is considered a number in the Unicode character database
>>> int('V', 32)
31
>>> int('１００', 2)
4
Binary → integer object
>>> int.from_bytes(b'\x00\xff', byteorder = 'big') #Since it is a class method, call it as an int type method
255
# signed =True to convert the byte sequence to a 2's complement signed integer
>>> int.from_bytes(b'\xfe\xff\xff\xff', byteorder = 'little', signed=True)
-2
Integer object method
#Get byte sequence of integer values
>>> (255).to_bytes(2, byteorder = 'big')
b'\x00\xff'
#Converted as 2's complement
>>> (-2).to_bytes(4, 'little', signed = True)
b'\xfe\xff\xff\xff'
#Returns the number of bits required to convert a number to a binary number (sign bit not included)
>>> (100000000).bit_length()
27
Logical value type
#Derived from an integer type, True is actually an integer 1 and False is an integer 0.
>>> int(True)
1
>>> int(False)
0
#Can perform the same operations as ordinary integers
>>> True + False
1
>>> True * False
0
>>> False - 1
-1
>>> True + 1
2
>>> True / 2
0.5
Logical value object
#Logical value object is a bool type object
#There is always only one True object and one False object each
>>> bool(0)
False
>>> bool(1)
True
>>> bool([100])
True
>>> bool([])
False
>>> bool()
False
Bit inversion
# ~x is-1*(x+1)Returns an integer value that is (Python does not perform bit operations internally)
>>> ~5
-6
>>> ~(-6)
5
>>> '{:08b}'.format(5 & 0xff)
'00000101'
>>> '{:08b}'.format(-6 & 0xff)
'11111010'
Infinity / non-number in floating point arithmetic
#If the floating point value is greater than the valid range
>>> 1e200 * 1e200
inf #Infinity is displayed as inf
>>> -1e200 * 1e200
-inf
#The result is a non-number (Not A Number), such as when operating with an infinite value.:When it becomes NaN)
>>> 0 * 1e1000
nan
#The value is inf,nan floating point number is float()Create with method
>>> float('nan') #Non-number
nan
>>> float('inf') #Infinity
inf
>>> float('-inf') #Negative infinity
-inf
>>> float('infinity') # 'infinity'Infinite
inf
Floating point object methods
#Returns a tuple of two integer values whose ratio is the same as the value of the object. The second value is always positive.
>>> (0.5).as_integer_ratio()
(1, 2)
>>> (-2.5).as_integer_ratio()
(-5, 2)
# inf,The following exception is thrown for nan
>>> float('inf').as_integer_ratio()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OverflowError: Cannot pass infinity to float.as_integer_ratio.
>>> float('nan').as_integer_ratio()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: Cannot pass NaN to float.as_integer_ratio.
#Output the value of the object as a character string in hexadecimal format
# [sign]['0x']integer['.'fraction]['p'exponent]Created in format
>>> 1.0.hex()
'0x1.0000000000000p+0'
#Returns True if the value has a decimal point of zero and is an integer value other than inf or nan
>>> (-2.0).is_integer()
True
>>> (3.2).is_integer()
False
>>> float('inf').is_integer()
False
>>> float('nan').is_integer()
False
Decimal floating point number
#Calculations with floating point numbers are generally inaccurate
>>> 0.3 - 0.2
0.09999999999999998
#Python provides a decimal module for decimal floating point arithmetic
#Unlike float type calculations, all calculations are done by software, so performance is degraded.
>>> import decimal
>>> print(decimal.Decimal('0.3') - decimal.Decimal('0.2'))
0.1
# inf, nan
>>> from decimal import Decimal
>>> Decimal('inf')
Decimal('Infinity')
>>> Decimal('nan') + 1 #The result of the operation with nan is nan,
Decimal('NaN')
>>> Decimal('sNaN') + 1 #An exception can be raised by using a special value called signaling NaN.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
decimal.InvalidOperation: [<class 'decimal.InvalidOperation'>]
Recommended Posts