Python, Theory

Python. Numbers. Representation of numbers of different types. Basic numeric types. Number conversion functions




Numbers. Representation of numbers of different types. Basic numeric types. Number conversion functions

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1. Categories of numeric types

In Python, number types are represented by the following categories:

  • ordinary numeric types (real, integer);
  • literals (create numeric types);
  • expressions (processing of numeric types).

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2. List of numeric types

The following numeric types are supported in Python:

  • integers and real numbers;
  • complex numbers;
  • fixed precision numbers;
  • rational numbers;
  • sets
  • logical values;
  • integers of unlimited precision.

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3. Representation of integers (literals) in different calculus systems. Example

Integers (or integer literals) can be written in different calculus systems:

  • decimal format;
  • hexadecimal;
  • octal;
  • binary.

Example. Writing the number (literal) 30 in various formats

30 # decimal format
0x1e # hexadecimal
0X1E # hexadecimal
036 # octal, Python 2.6
0B11110 # binary
0b11110 # binary
0O36 # octal, Python 3.0
0o36 # octal, Python 3.0

If you try to represent an octal value in Python 3.0, as in Python 2.6 (036), the compiler will throw an error.

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4. Types of integers in Python 2.6: regular and long. Example

In Python 2.6, integers can be represented by two types:

  • regular (32-bit) numbers;
  • long (unlimited precision) numbers. Such numbers end with the character l or L. If the numeric value of an integer literal does not fit into a regular 32-bit number, then this value is automatically cast to a long integer. In this case, the interpreter automatically performs the corresponding conversion.

Example.

12345 # regular 32-bit number
1234567890l # long number in Python versions up to 3.0
7777777777777L # long number in Python versions up 3.0

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5. Representation of integers in Python 3.0

In Python 3.0, both types of numbers (regular and long) were represented as a single (single) type of integers, which is automatically represented as a long integer (supports unlimited precision). Therefore, in this version of Python there is no need to complete literals with l or L. If you specify l or L after the number in Python 3.0, the interpreter will throw an “Invalid token” error.

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6. Conversion functions of the numbers in the string, and vice versa hex(), oct(), bin(), int(). Examples

The following functions are used to turn the numeric form of a literal into a string:

  • hex(num) – converts the number num to a string that displays this number in hexadecimal notation;
  • oct(num) – converts the number num into a string that represents this number in octal;
  • bin(num) – converts the number num to a string that represents this number in binary.

To convert a string to an integer taking into account the calculus system, use the function

int(s, base)

here

  • s – a string;
  • base – an integer that determines the number of digits in the number system. For example, for calculus 7, the value base = 7.

Examples of conversion functions.

sh = hex(15) # sa = 0xF
so = oct(15) # sb = 0o17
sb = bin(15) # sb = 0b1111

i = int('15',10) # i = 15
i = int('15',8) # i = 13
# i = int('19',8) - error, the number 9 cannot be in the 8th calculus

i = int('2EF',16) # i = 751
i = int('20',16) # i = 32
i = int('14',5) # i = 9

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7. Representation of real numbers. Example

Real numbers define floating point numbers. Real numbers (literals) can be represented as:

  • numbers that contain the separator of the integer and fractional part;
  • numbers that contain the character e or E to indicate the order of the number.

The Python interpreter recognizes a real number by the presence of the character ‘.’ (“dot”) or exponent (e or E). After the number is recognized, the corresponding object of a real type is created. Such an object is used in further mathematical expressions as an object of a real type (and not an object of an integer or another type).

Example.

2.85 # ordinary representation of a real number
3. # number 3.0
1.3e-3 # number 0.0013
1.52E6 # 1520000.0
3e2 # 300.0
2.0E-1 # 0.2

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8. Complex numbers. Examples

Python has the ability to work with complex numbers. The general form for representing a complex number is as follows:

real_part + imag_part j

here

  • real_part – the real part of the complex number, which is optional (in the case when the number does not contain the real part);
  • imag_part – the imaginary part of the complex number, which ends with the character j or J.

The interpreter represents a complex number as two real numbers. When used in mathematical expressions, complex numbers are processed accordingly.

Examples of complex number literals

6-8j
2.5+3.8j
0.001J
2.-3.J

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9. Creating complex numbers. Function complex(). Example

Complex numbers are created by the complex() function, which is a built-in Python function. General form of function:

complex(real, imag)

Example.

a = complex(6, -8) # a = (6-8j)
b = complex(0, 2.5) # b = 2.5j
c = complex(0.02, -1e4) # c = (0.02-10000j)

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10. The eval() function. Converting a string to number

A number can be represented as a string, for example

'258'
"0x2A5"

You can use the eval() function to convert a string to a number. The eval(s) function considers the string s as Python code. The function compiles the string s and uses it. The string is considered as part of the program.

Example.

# Function eval()
# execution of a line as program code
a = 5
b = 6
c = eval('a+b') # c = a+b = 11

# converting strings represented as a number to the number itself
c = eval('0xF5') # c = 245
c = eval('0b111') # c = 7
c = eval('0o135') # c = 93

d = bin(eval('0b101')) # d = 0b101

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Related topics

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