Javascript Remove N From String

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The slicing syntax allows you to remove a particular character or a range of characters from a string based on the index values ‚Äã‚Äãof those characters.

This guide explains how to remove the first n characters from a string in Python. Give an example of the slicing syntax so that you can learn how to use it in your programs.

Python: indexing strings

Strings are sequences of characters . Each character in a string is assigned a unique index number . This number allows you to identify and work with a specific character or set of characters.

Index numbers start with zero and gradually increase by one for each character. Let’s look at a string:

P i and s !
1 2 3 4

The chain contains four characters. The first character, "P", has the index number 0. The last character, !, has index number 4.

You can use these numbers to retrieve single characters or remove characters from a string.

Remove the first n characters from a string in Python

Here, write a program that removes the first four characters from receipts stored by a donut shop. These characters represent the ID of a purchase but are no longer relevant due to a system update.

To start, set a receipt list and a new list to store new receipts:

The three digits at the top of the list are the purchase ID. There is also a space after the ID you want to remove.

Use a "for" loop to scroll through each receipt in the list so you can delete the first four characters of each receipt:

This code removes the first four characters of each receipt in "receipts & rdquo; listing. A new string without these characters is assigned to the variable "new_r" with the corresponding characters removed. You do this because the strings are immutable and you cannot modify an existing string.

Then add the new receipt to the "new_receipts" list Finally, print the "new_receipts" list to the console so you can see if the code worked:

Run the code and see what happens:

The code successfully removed the first four characters from each of the original strings.

If you want to remove more or less characters, you need to replace the number 4 by the number of characters you want to delete To delete only the two first first characters of strings, use this code:

With this line of code, the program would return:

Conclusion

You can delete the first n characters of a string using section syntax. This syntax allows you to retrieve a particular part of a string based on a particular index value.

You now have the knowledge to use slicing to remove characters from the start of a string. Python like a professional programmer !

Javascript Remove N From String __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Javascript Remove N From String __delete__: Questions

2639

Answer #2


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #3

Python syntax to delete a file

import os
os.remove("/tmp/<file_name>.txt")

Or

import os
os.unlink("/tmp/<file_name>.txt")

Or

pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()

Path.unlink(missing_ok=False)

Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

#!/usr/bin/python
import os
myfile="/tmp/foo.txt"

## If file exists, delete it ##
if os.path.isfile(myfile):
    os.remove(myfile)
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

#!/usr/bin/python
import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
try:
    os.remove(myfile)
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))

RESPECTIVE OUTPUT

Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder

shutil.rmtree()

Example for shutil.rmtree()

#!/usr/bin/python
import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
try:
    shutil.rmtree(mydir)
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "D:zjm_codea.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

But is there not a simpler way to do this?

1055

Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]

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