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This article focuses on "how to use Python strings". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Now let the editor take you to learn how to use Python strings.

Some case examples 1: design a function that generates a CAPTCHA of a specified length.

Description: the CAPTCHA consists of numbers and uppercase and lowercase letters.

Import random

ALL_CHARS = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

Def generate_code (code_len=4):

Generate a CAPTCHA of a specified length

: param code_len: length of the CAPTCHA (4 characters by default)

Return: a random CAPTCHA string consisting of uppercase and lowercase letters and numbers

""

Code =''

For _ in range (code_len):

# generate random numbers in the range from 0 to string length minus 1 as index

Index = random.randrange (0, len (ALL_CHARS))

# use index operation to extract characters from a string and splice them together

Code + = ALL_ chars [index]

Return code

We use the following code to generate 10 sets of random verification codes to test the above functions.

For _ in range (10):

Print (generate_code ())

There is actually a simpler way to write the above function, which directly uses the random sampling function of the random module to extract a specified number of characters from the string, and then uses the join method of the string to concatenate the selected characters. In addition, you can use the string module in the Python standard library to obtain literal constants of numbers and letters.

Import random

Import string

ALL_CHARS = string.digits + string.ascii_letters

Def generate_code (code_len=4):

Generate a CAPTCHA of a specified length

: param code_len: length of the CAPTCHA (4 characters by default)

Return: a random CAPTCHA string consisting of uppercase and lowercase letters and numbers

""

Return'. Join (random.choices (ALL_CHARS, k=code_len))

Note: both the sample and choices functions of the random module can achieve random sampling, and sample can achieve no return sampling, which means that the characters sampled are not repeated; the choices implementation has put back sampling, which means that some characters may be repeatedly selected. The first parameter of these two functions represents the population sampled, while the parameter k represents the number of samples.

Example 2: design a function to return the suffix name of a given file name.

Description: the file name is usually a string, and the suffix name of the file refers to the last of the file names. The latter part, also known as the file extension, is a mechanism used by some operating systems to mark file types. For example, on Windows systems, the suffix exe indicates that this is an executable program, and the suffix txt indicates that this is a plain text file. It is important to note that on Linux and macOS systems, the file name can be. At the beginning, it indicates that this is a hidden file, a file name like .gitignore. This file does not have a suffix name or suffix name''.

Def get_suffix (filename):

"" gets the suffix name of the file name

: param filename: file name

: return: the suffix name of the file

""

# look in reverse from the string. Where it appears.

Pos = filename.rfind ('.')

# remove the suffix from the file name by slicing

Return filename [pos + 1:] if pos > 0 else''

You can use the following code to do a simple test on the above function.

Print (get_suffix ('readme.txt')) # txt

Print (get_suffix ('readme.txt.md')) # md

Print (get_suffix ('.readme')) #

Print (get_suffix ('readme.')) #

Print (get_suffix ('readme')) #

The above get_suffix function also has a more convenient way to implement, is to directly use the os.path module's splitext function, this function will split the file name into two parts with the path of the file name and extension, and then return a binary (tuple will be discussed in the next lesson), the second element in the binary is the file suffix name (including.), if you want to remove the suffix name. You can do a string slicing operation, as shown below.

From os.path import splitext

Def get_suffix (filename):

Return splitext (filename) [1] [1:]

Example 3: display racing lantern (scrolling) text in the terminal.

Description: the principle of realizing the racing lantern text is very simple: put the first character of the current string at the end of the content to be output, and the content after the second character to the front of the content to be output. you can see the scrolling text by repeating this operation in a loop. The interval between the two loops can be realized by the sleep function of the time module, and the previous output on the screen can be cleared by using the system function of the os module to call the system screen cleaning command.

Import os

Import time

Content = 'Beijing Huan welcomes you to open up heaven and earth for you'

While True:

# Windows clears the output on the screen

# os.system ('cls')

# macOS clears the output on the screen

Os.system ('clear')

Print (content)

# hibernate for 0.2 seconds (200 milliseconds)

Time.sleep (0.2)

Content = content [1:] + content [0]

Tip: we suggested that you temporarily use VS Code to write Python code and run Python programs in the "command prompt" or "terminal". If you have already started using PyCharm in advance, you need to remind you that the running window of PyCharm is useless. To see how the above code works, it is recommended to run the program in the command line prompt or terminal.

At this point, I believe you have a deeper understanding of "how to use Python strings". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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