Python two articles computer knowledge (data type)

Basic data types

Digital Type

Python language provides three numeric types: type integer, floating-point type and complex type, respectively mathematics integer, real and complex.

Integer type

Ary species	Pilot symbols	description
Decimal	no	By default, for example: 1010, -1010
Binary	0b or 0B of characters 0 and 1,	Example: 0b1010, 0B1010
Octal	0o or 0O composed by the characters 0 to 7,	Example: 0o1010, 0O1010
Hex	0x or 0X by the characters 0 to 9, a to f or compositions A to F,	Example: 0x1010

Floating point numbers
represented in decimal form and generally represent scientific notation: There are two floating-point representation. In addition to decimal, binary floating-point number that no other representation
-1.3e3 -2.5E5
Complex types
- Python language, can be seen as a plurality of binary ordered pair of real numbers (A, b), expressed as: a + bj, where, a is a real part, referred to as a real part, b is the imaginary part, referred to as the imaginary part. Imaginary part "J" or "j" is represented by suffix. Note that when b is 1, 1 can be omitted, i.e. 1j represents a complex, and the variable j indicates a Python program.
- Type complex real and imaginary part is a floating point, for a plurality of Z, it is possible to obtain a real part and an imaginary part, respectively, with z.real and z.imag

Python provides nine basic value operator that

Operators	description
x + y	and the sum of x and y
x - and	The difference between x and y
x * y	The product of x and y
x / y	x and y quotient
x // and	Integer quotient of x and y, namely: List of x and y is no greater than the maximum integer
x% and	I quotient of x and y, also known as modular arithmetic
-x	x is negative, that: x * (- 1)
+x	x itself
x ** and	x to the power y, i.e.: xy

Numerical calculation result may change the data type, and the types of changes related to the operator, the following basic rules:

Mixed integer and floating point arithmetic, floating-point result is output;
Operation between integers, the result type associated with the generation operator, / is the result of floating point operation;
And a plurality of integer or floating point operation, the output plural.

Built-in functions

function	description
abs(x)	Absolute value of x
divmod(x, y)	(X // y, x% y), the output in the form of a binary group (also referred to as a tuple type)
pow(x, y[, z])	(X y)% z, [..] indicates that the parameter can be omitted, namely: pow (x, y), which is the same x y
ound(x[, ndigits])	X rounded to retain ndigits decimal places. round (x) returns the integer values rounded
max(x1, x2, …, xn)	x1, x2, ..., xn to a maximum value, n is not limited
min(x1, x2, …, xn)	x1, x2, ..., xn of the minimum value, n is not limited

String type

Python language escape character:

\ N newline, \ represents a backslash 'represents a single quotation mark "represents double quotes, \ T for a tab (TAB) and the like.

String operator

Providing several basic operators for string, Python language

Operators	description
x + y	Connecting the two strings x and y
x * n or n * x	Copy the string x n times
x in s	If x is a substring of s, returns True, otherwise False

>>>name = "Python语言" + "程序设计"
>>>name
'Python语言程序设计'
>>>"等级考试!" * 3
'等级考试!等级考试!等级考试!'
>>>"语言" in name
True
>>>'Y' in name
False

String handling functions
Python language provides a number of built-in functions for string handling

function	description
len (x)	Returns the length of the string x, and returns the number of elements may also be other combinations of data types
str(x)	Returns a string corresponding to any type of x
chr(x)	Returns Unicode encoding single character corresponding to x
words (x)	Unicode character encoding single return x represented
hex(x)	Returns the integer x corresponding to the lowercase hexadecimal string
oct(x)	Returns the integer x corresponding to the octal string lowercase
am (x)	Returns the integer x corresponding to the binary string lowercase

>>>len("全国计算机等级考试Python语言科目")
19
>>>chr(10000)
'✐‘
>>>hex(1010)
'0x3f2'

String processing method

method	description
str.lower()	Returns the string str copy all lowercase characters
str.upper()	Returns a copy of the string str, all uppercase characters
str.split(sep=None)	It returns a list, according to a sep divided portions constituting str
str.count(sub)	Returns the number of sub substring appears
str.replace(old, new)	Returns a copy of string str, all old substring is replaced with a new
str.center(width, fillchar)	字符串居中函数， fillchar参数可选
str.strip(chars)	从字符串str中去掉在其左侧和右侧chars中列出的字符
str.join(iter)	将iter变量的每一个元素后增加一个str字符串

# split()
>>>"Python is an excellent language.".split()
['Python', 'is', 'an', 'excellent', 'language.']
>>>"Python is an excellent language.".split('a')
['Python is ', 'n excellent l', 'ngu', 'ge.']
>>>"Python is an excellent language.".split('an')
['Python is ', ' excellent l', 'guage.']

# count()
>>>"Python is an excellent language.".count('a')
3

# replace()
>>>"Python is an excellent language.".replace('a', '#')
'Python is #n excellent l#ngu#ge.'
>>>"Python is an excellent language.".replace('Python', 'C')
'C is an excellent language.'

# center()
>>>"Python".center(20, "=")
'=======Python======='
>>>"Python".center(2, "=")
'Python'

# str.strip(chars)
# 从字符串str中去掉在其左侧和右侧chars中列出的字符。 chars是一个字符串，其中出现的每个字符都会被去掉。
>>>"   ==Python==   ".strip(' ')
'==Python=='
>>>" ==Python== ".strip(' =')
'Python'
>>>" ==Python== ".strip(' =n')
'Pytho'

# str.join(iter)中iter是一个具备迭代性质的变量， 该方法将str字符串插入iter变量的元素之间， 形成新的字符串
>>>" ".join('PYTHON')
'P Y T H O N'
>>>",".join('12345')
'1,2,3,4,5'
>>>",".join(['1', '2', '3', '4', '5'])
'1,2,3,4,5'

format()方法的使用

字符串format()方法的基本使用格式是：
<模板字符串> .format( <逗号分隔的参数> )

>>>"{}曰： 学而时习之， 不亦{}。 ".format("孔子","说乎")
'孔子曰： 学而时习之， 不亦说乎。 '
>>>"{1}曰： 学而时习之， 不亦{0}。 ".format("说乎","孔子")
'孔子曰： 学而时习之， 不亦说乎。 '

format()方法的格式控制
format()方法中模板字符串的槽除了包括参数序号，还可以包括格式控制信息。
{ <参数序号> : <格式控制标记> }
其中，格式控制标记用来控制参数显示时的格式。格式
控制标记包括： <填充> <对齐> <宽度> ******<.精度> <类型> 6个字段，这些字段都是可选的，可以组合使用

>>>s = "等级考试"
>>>"{:25}".format(s) #左对齐， 默认
'等级考试               '
>>>"{:^25}".format(s) #居中对齐
'          等级考试        '
>>>"{:>25}".format(s) #右对齐
'                  等级考试'
>>>"{:*^25}".format(s) #居中对齐且填充*号
'**********等级考试***********'
>>>"{:+^25}".format(s) #居中对齐且填充+号
'++++++++++等级考试+++++++++++'
>>>"{:十^25}".format(s) #居中对齐且填充汉字“十”
'十十十十十十十十十十等级考试十十十十十十十十十十十'
>>>"{:^1}".format(s) #z指定宽度为1， 不足变量s的宽度
'等级考试

<.精度>由小数点（.）开头。对于浮点数，精度表示小数部分输出的有效位数。对于字符串，精度表示输出的最大长度。小数点可以理解为对数值的有效截断

>>>"{:.2f}".format(12345.67890)
'12345.68'
>>>"{:>25.3f}".format(12345.67890)
' 12345.679'
>>>"{:.5}".format("全国计算机等级考试")
'全国计算机'

<类型> 表示输出整数和浮点数类型的格式规则。
对于整数类型，输出格式包括6种：
• b: 输出整数的二进制方式；
• c: 输出整数对应的Unicode字符；
• d: 输出整数的十进制方式；
• o: 输出整数的八进制方式；
• x: 输出整数的小写十六进制方式；
• X: 输出整数的大写十六进制方式；

>>>"{0:b},{0:c},{0:d},{0:o},{0:x},{0:X}".format(425)
'110101001,Ʃ,425,651,1a9,1A9'

对于浮点数类型，输出格式包括4种：
• e: 输出浮点数对应的小写字母e的指数形式；
• E: 输出浮点数对应的大写字母E的指数形式；
• f: 输出浮点数的标准浮点形式；
• %: 输出浮点数的百分形式。

>>>"{0:e},{0:E},{0:f},{0:%}".format(3.14)
'3.140000e+00,3.140000E+00,3.140000,314.000000%'
>>>"{0:.2e},{0:.2E},{0:.2f},{0:.2%}".format(3.14) # 对比输出 
'3.14e+00,3.14E+00,3.14,314.00%'

数据类型转换

Python语言提供type(x)函数对变量x进行类型判断，适用于任何数据类型

n = eval(input('请输入一个数字:'))
if type(n) == type(123):
print("输入的数字是整数。 ")
elif type(n) == type(11.3):
print("输入的数字是浮点数。 ")
else:
print("无法判断输入类型。 ")

数值运算操作符可以隐式地转换输出结果的数字类型，例如，两个整数采用运算符“/”的除法将可能输出浮点数结果。
此外，通过内置的数字类型转换函数可以显式在数字类型之间进行转换

函数	描述
int(x)	将x转换为整数， x可以是浮点数或字符串
float(x)	将x转换为浮点数， x可以是整数或字符串
str(x)	将x转换为字符串， x可以是整数或浮点数

Python two articles computer knowledge (data type)

Python two articles computer knowledge (data type)

Basic data types

Digital Type

String type

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