Variables and data types in Python

Python is a language with weak data types. Variables can be used without declaration. Assigning a value to a variable means defining the variable. The type of the value assigned is the type of the variable, but the variable also has a data type, string '1 'If you want to participate in data calculation, you need to use the int() function for conversion, and use the type() function to view the data type of the variable.

Variables store references to the memory addresses of data. Variables in Python are divided into unmodifiable variables and modifiable variables. Unmodifiable variables include int, float, and str strings. , tuple tuples, etc. Modifiable variables include list list, dict dictionary, set collection, etc. When passing parameters to a function, python always passes a reference to the value. However, if the value passed is an unmodifiable variable, a copy will be passed to the function because it cannot be modified. How can the value passed be a modifiable list or dictionary? etc., then the references to these values ​​are passed directly and can be modified within the function body.

Data types in python:

String: A sequence of characters enclosed in single or double quotes. To use variables in a string, you can use f string. This is a newly introduced function in python3.7. It is very convenient to use. Add f before the first quotation mark of the string, and you can use { in the string. } Curly braces insert variables into the string, such as f"thisis a {cat}", where cat is a variable name.

Numeric type: Integer int, dot number float, numerical type can be added, subtracted -, multiplied *, divided /, exponentiated** , take the remainder % and other operations.

List: A collection of ordered and modifiable data enclosed in square brackets [] and separated by commas. For example, [1,2,3,4,5], add elements in the list using the appand() method, insert elements using the insert() method, and delete elements using the del statement, pop() method or remove() method. The sort() method is used to sort the list, the sorted() method is used for temporary sorting, the reverse() method is used for reverse order, the len() method is used to obtain the length of the list, and the for...in... statement is used to traverse the list.

Tuple: A list is a modifiable data collection, while a tuple is an immutable list, a set of data collections enclosed in parentheses () and separated by commas.

Dictionary: The dictionary is a data collection of a series of key-value pairs, enclosed in curly braces {}, and separated by commas. The key-value pairs are separated by colons: , each key is associated with its value, which can be any data type, even a list or dictionary itself. Some operations on dictionaries are very similar to lists. You can use the get() method to obtain a key-value pair that may not exist.

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