NLP | Storing an ordered dictionary in Redis

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class RedisOrderedDict (collections.MutableMapping):

  

  def __ init__ ( self , r, name):

self ._ r = r

self ._name = encode_key (name)

  

def __ iter __ ( self ):

return iter ( self . items ())

 

def __ len __ ( self ):

return self ._r.zcard ( self ._ name)

 

  def __ getitem __ ( self , key):

return self ._ r.zscore ( self . _name, encode_key (key))

 

  def __ setitem __ ( self , key, score):

self ._r.zadd ( self ._ name, encode_key (key), score)

 

def __ delitem __ ( self , key):

self ._ r.zrem ( self ._ name, e ncode_key (key))

 

def keys ( self , start = 0 , end = - 1 ):

# we use zrevrange to sort keys

  # by value instead of

lowest

return self ._ r.zrevrange ( self ._ name, start, end)

  

def values ​​( self , start = 0 , end = - 1 ):

return [v for (k, v) in self . items (start = start, end = end)]

 

def items ( self , start = 0 , end = - 1 ):

  return self ._ r.zrevrange ( self ._ name, start, end, withscores = True )

  

  def get ( self , key, default = 0 ):

return self [key] or default

 

def iteritems ( self ):

return iter ( self )

 

def clear ( self ):

  self ._ r.delete ( self ._ name)

Code: Create a RedisOrderedDict instance by passing a Redis connection and unique name

Exit :

 0 5.2000000000000002 1 [(b`bar`, 5.2)] 

Most of the code might look similar to RedisHashMap, which is to be expected since they both extend collections . The main difference is that RedisOrderedSet orders keys by floating point values, and therefore is not suitable for arbitrary storage of key values ​​such as RedisHashMap
Sketches explaining each key method and how they work with Redis:

  • __len __ (): the zcard command is used to get the number of items in an ordered set.
  • __getitem __ (): uses the zscore command to get the score for a key and returns 0 if the key does not exist.
  • __ setitem __ (): this command uses the zadd command to add a key to the ordered set with a given score, or update the score if the key already exists.
  • __delitem __ (): The zrem command is used to remove a key from the ordered set.
  • keys (): The zrevrange command is used to get all the keys in the ordered set sorted by the highest score. To get a snippet of ordered keys more efficiently requires two optional keyword arguments, start and end.

NLP | Storing an ordered dictionary in Redis __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:

NLP | Storing an ordered dictionary in Redis __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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from redis import Redis

from rediscollections import RedisOrderedDict

 

r = Redis ()

rod = RedisOrderedDict (r, `test` )

rod.get ( ` bar` )

  

rod [ `bar` ] = 5.2

print (rod [ `bar` ])

 

print ( len (rod))

 

print (rod.items ()) 

 
rod.clear ()