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<!DOCTYPE markdown>
{{tag>Code Python}}

# Draft Python3

## List comprehensions and generator expressions

 (short form: “listcomps” and “genexps”)

~~~python
line_list = ['  line 1\n', 'line 2  \n', ' \n', '']

# Generator expression -- returns iterator
stripped_iter = (line.strip() for line in line_list)

# List comprehension -- returns list
stripped_list = [line.strip() for line in line_list]

stripped_list = [line.strip() for line in line_list if line != ""]
~~~


### Autres

~~~python
def inc(f, id):
    """ Exemple : inc(lambda x : x+1, 0) """
    try :
        global counter
        counter = f(counter)
    except NameError:
        counter = 0
    return counter
~~~

------------

http://mgautier.fr/blog/Astuce/changer-lenvironnement-bash-avec-python.html

------------

## List unique remove duplicate

Source : 
http://stackoverflow.com/questions/89178/in-python-what-is-the-fastest-algorithm-for-removing-duplicates-from-a-list-so

~~~python
def unique(items):
    found = set([])
    keep = []
    for item in items:
        if item not in found:
            found.add(item)
            keep.append(item)
    return keep
~~~

------------

## How do you split a list into evenly sized chunks in Python?

Source : http://stackoverflow.com/questions/312443/how-do-you-split-a-list-into-evenly-sized-chunks-in-python

~~~python
def chunks(l, n):
    n = max(1, n)
    return [l[i:i + n] for i in range(0, len(l), n)]
~~~

-------------

## Determine if variable is defined in Python

http://stackoverflow.com/questions/1592565/determine-if-variable-is-defined-in-python

~~~python
try:
  thevariable
except NameError:
  print "well, it WASN'T defined after all!"
else:
  print "sure, it was defined."
~~~

I think it's better to avoid the situation. It's cleaner and clearer to write:

~~~python
a = None
if condition:
    a = 42
~~~

------------

## Getting file size in Python

http://stackoverflow.com/questions/6591931/getting-file-size-in-python

~~~python
def get_Size(file):
    file.seek(0,2) # move the cursor to the end of the file
    size = file.tell()
    return size
~~~

Exemple :
~~~python
with open('plop.bin','rb') as file:
    size=get_Size(file)

with open('plop.bin','rb') as file:
    #size=get_Size(file)
    for i in range(size):
        un, deux = read_hexafile()
        msg.append(un)
        msg.append(deux)
~~~


''/dev/null''
~~~python
fnull = open(os.devnull, 'w')
~~~

-----------------

## Message d'erreur 

How to print to stderr in Python?

http://stackoverflow.com/questions/5574702/how-to-print-to-stderr-in-python

~~~python
def warning(*objs):
    print(*objs, file=sys.stderr)
~~~

## Conversion hexa

~~~python 
import numpy as np

carac=re.sub('^','0x',carac)
carac= int(carac, 16)
print(carac)
file.write(np.byte(carac))


with open('plop.bin', 'bw') as file:
        file.write(b'\x50\x40\x73')
        
        
hex(11) # '0xb'

a = int('0x100', 16)
print(a)   #256
print('%x' % a) #100

import binascii
binascii.unhexlify('7061756c')  # b'paul'

"{0:8b}".format(int("a",16))    # '    1010'

~~~

http://stackoverflow.com/questions/16843108/how-to-read-a-hex-file-into-numpy-array
~~~python
with open(myfile) as f:
    iv = binascii.unhexlify(f.readline().strip())
    key = binascii.unhexlify(f.readline().strip())
    count = int(f.readline())
    a = np.fromiter((binascii.unhexlify(line.strip()) for line in f), dtype='|S16')
~~~


~~~python
hashlib.sha512('Bonjour'.encode('utf-8')).hexdigest()
hex(int.from_bytes('Bonjour'.encode('utf-8'), 'big'))
~~~

--------

Créer un Dictionnaire à partir de deux listes (l'une clef, l'autre valeur)

~~~python
clef = ['a', 'b', 'c']
valeur = [1, 2, 3]
dictionnaire=dict(zip(clef, valeur))
~~~

## Test

Voir :
* nox
* unittest

## Exception

http://stackoverflow.com/questions/16138232/is-it-a-good-practice-to-use-try-except-else-in-python

~~~python
try:
    s   
except NameError:
    pass
else: # If no exception occured, do :
    s.user.logout()
~~~



## Temps / time

Voir :
* timeit

~~~python
start = time.time()
UnifiedJob.objects.filter(id=1096679).update(status='canceled')
end = time.time()

print(end - start)
~~~

## Strings

https://zerokspot.com/weblog/2015/12/31/new-string-formatting-in-python/

## Debug

Source : https://www.geekarea.fr/wordpress/?p=763

Level 1
~~~python
f = open('/tmp/debug','a')
f.write(variable + '\n')
f.close()
~~~

Level 2
~~~python
from pprint import pprint
pprint(variable.__class__.__name__, f)
pprint(dir(variable), f)
pprint(vars(variable), f)
~~~

Level 3 (sur une exception)
~~~python
import traceback
f.write(str(traceback.format_exc()))
~~~


## map reduce filter

Voir : 
* [[notes_python_multithreading|Alternatives Multi threads à map]]


## Aures

A noter que sur RedHat 8 le chemin vers python est ''/usr/libexec/platform-python''