jupyter notebook for python (二)
(一)
字符串(string):
A String is a common type of data, used in programming, consisting of a sequence of 1 or more characters.
-
A String is a sequence of characters (aka: a string of characters)
- Character examples:
A, B, C, a, b, c, 1, 2, 3, !, &
- Character examples:
- A String in python is contained in quotes, single(') or double(")
- String examples: "ABC", 'Joana Dias', 'I have 2 pet cats.', "item #3 cost $3.29 USD"
Note: the quotes containing a string must come in matched pairs
-
"Hello"
or'Hello'
are correctly formatted strings -
"Hello'
is incorrectly formatted starting with double " and ending with single ' python needs a matching quote to know where the string ends
-
- String examples: "ABC", 'Joana Dias', 'I have 2 pet cats.', "item #3 cost $3.29 USD"
示例图:
(二)
整数型(Integers):
#A integers is another type:
- whole numbers such as
-2, -1, 0, 1, 2, 3
are Integers - Integers are not placed in quotes
A String can contain any character, this includes letters, spaces, punctuation, number digits and formatting. In a string with digits ("123"
) the digits are text images rather than representations of numeric values.
remember a line of python code starting with the pound or hash symbol (#*) indicates a *comment
comments are for humans to read and are not run by computers
示例图:
(三)
赋值:
Variables & Storing Strings in Variables:
单词翻译:
总结:我就把它当成一个变量,然后被赋值,打印输出的结果一样。
详情:
Variables are named containers
Computer programs often create storage for things that are used in repeated processing like item_price, student_name, stock_symbol. In python a variable is a type of object that can be addressed by name to access the assigned contents.
Name a variable staring with a letter or underscore "_"
There are different styles for creating variables this course uses lowercase descriptive names connected by underscores:
- item_price
- student_name
- stock_symbol
descriptive names reduce the need for comments in the code and make it easier to share code or read code written long ago
Variables can hold strings
once a variable is assigned:
current_msg = "I am a string"
a python program can refer to the variable, current_msg
, in code
so that current_msg
, can be used like the string value ("I am a string"
) which it stores
Variable reassignment
We can reassign a variable, changing the contents. current_msg = "new current message"
Variables can be used in place of literals
If we initialize current_msg = "new current message"
then
the literal string "new current message"
and the variable current_msg
are the same when used in code
(四)
(变量可以重复使用,并被覆盖)
Data types in variables:
实例图:
(图中的任务只是改写例子的名字就ok了)
详情:
variables can be initialized with different data types. Below we see item_price is a decimal(aka - float) and student_name is string
item_price = 10.25 #item_price initialized as a numeric value (no quotes)
student_name ="Dias, Joana" #student_name initialized as a string
license_plate = "123A" #license_plate initialized as a string
Variables can start initialized as an Integer number data type
x = 22
here the Integer
22
value was assigned to the variablex
The type of data a variable holds can be changed,
Python variables can change the type of data a variable holds
x = 22 x = "I am a string"
x
changed type from Integer x = 22
to string x = "I am a string"
Best Practice: Friendly Names Friendly name examples, ( item_price, student_name,license_plate
), were used above.
Variables help us to write code that can be used repeatedly
A personalized letter can be sent to every student with individual names by using a name in a variable. Let's start with printing a name based on string variable.
Create a variable, name
, at the top of the next cell. Assign a string value to name
.
Remember to use the quotes for string values
example:
name = "Joana Dias"
print(name)
翻译: