Python
From Torben's Wiki
Contents |
Basics
# delete a variable del var # check if variable is defined if xyz in locals() : # for object oriented projects: if "xyz" in self.__dict__.keys():
Strings
# num <-> str
s= str (i) # int to string
f = float("1.234") # str -> float
str(round(f, 1)) # round first
text = text.strip() # trim spaces
text = prompt("Enter Text: ") # get string from prompt
print "Renner =", i
# handling substrings
a = "abcd"
b = a[:1] + "o" + a[2:]
> 'aocd'
# find a substring:
x in s
> True / False
s * 5
>>> s+s+s+s+s
s.replace(x, y)
# convert int i to string with leading zeros if i<100
print "%03d" % (i)
# place formatted numbers in a string / sprintf
"The %i %s cost %f euros" % (3, "beers", 11.50)
> 'The 3 beers cost 11.500000 euros'
"The length is %.2f meters" % 72.8958
>'The length is 72.90 meters'
p= "%.1f%%/min" % precent
Find a substring
myString="Hello there !bob@"
mySubString=myString[myString.find("!")+1:myString.find("@")]
the string lib
import string string.capwords(s) # upper case first letter of each word and also removes multiple and trailing spaces
Lists
like arrays in Perl
L = [1,2,3,4,5,6]
L = [x for x in range(10)]
L = s.split () # split string s by spaces, use (s.split(",")) to split on "," etc
len(L)
L[0:10] # get elements 0-10
M = L[:] # copy L
M = L # link list M->L
L.append(x) # append a single element
L.extend(M) # put elements of list M to the end of List L
L.insert(i, x) # insert item x at position int i
L.pop() # returns and removes the last item
L.pop(i) # returns and removes the item at position int i
L.reverse()
L.sort()
L.remove(x) # removes the first occurrence of item x
L.count(x) # how many items x are in the list
L.index(x) # gives the position of the first x in list
s="".join(L)
x in L
x not in L
# List to string
"\n".join(L)
Tupels
Ordered sequence, with no ability to replace or delete items
L = (1,2,3,4,5,6)
Dictionaries
like hash in Perl
d = {'keyx': valuex, 'keyy': valuey}
d['keyz'] = valuez
tel.keys()
['keyx', 'keyy', 'keyz']
del d['keyy']
len(d)
d.clear()
d.copy()
d.keys()
d.values()
d.items() # returns a list of tuples (key, value)
d.get(k) # returns value of key k
d.get(k, x) # returns value of key k; if k is not in d it returns x
d.pop(k) # returns and removes item k
d.pop(k, x) # returns and removes item k; if k is not in d it returns x
x in d
x not in d
Loops
while i <= 100:
...
if sth:
break
for i in range(1, 5):
print i
if sth:
continue
else:
print 'The for loop is over'
for f in files :
Imports
import sys
import datetime
import time
import math
import random
import os.path
import MyFile # without tailing .py
# import a file, not stored in the same folder
import sys
sys.path.append("../MyPyLibs") # here we find ipHelp.py and Devices.py
Math
get rid of the annoying integer division: [1]
from __future__ import division
Date and Time
http://pleac.sourceforge.net/pleac_python/datesandtimes.html
import datetime
d = datetime.date.today().strftime("%y%m%d")
d = datetime.datetime.today().strftime("%y%m%d-%H%M")
sleep for a while
import time time.sleep(60)
wait for user input
raw_input("Press Enter to close")
calculate time
import time duration = 1234 # sec print "ETA =",time.ctime(time.time()+duration) array = time.localtime(time.time()+duration)
File Access
http://www.penzilla.net/tutorials/python/fileio/
Get filename of python script
from sys import argv myFilename = argv[0]
Read filename from commandline parameter
import sys for filename in sys.argv:
Write to file
filename = "test.dat" FILE = open(filename,"w") # w = overWrite file ; a = append to file FILE.writelines(list) # or for line in list: FILE.write(line) FILE.close()
Force update of filecontents without closing it
FILE.flush()
Read file
FILE = open(filename,"r") list = FILE.read() # or line = FILE.readline() FILE.close()
Touch file
if os.path.exists(fname): os.utime(fname, None) else: open(fname, 'w').close()
Read Timestamp (last modified)
lasttime = os.path.getmtime(fname)
Check if file / dir exists
import os.path # os.path - The key to File I/O
os.path.exists("text.txt")
os.path.isfile("text.txt")
os.path.isdir("text")
os.path.isabs("/home/torben/text.txt") # Is it an absolute path
make dirs
if not os.path.isdir(d) : os.mkdir(d) # normal os.makedirs(d) # recursively= with all parents
Delete folder+contents
import shutil shutil.rmtree(d)
Cross platform paths
currentdir = os.curdir mysubdir = os.path.join(currentdir, "mysubdir")
Get list of files (not dirs) in directory
dirname = "/path/to/some/dir" listoffiles = [ f for f in os.listdir(dirname) if os.path.isfile(dirname+"/"+f) ] listoffiles.sort()
Get file size
import os
int (os.path.getsize("moinsen.txt") )
Split path into folder, filename, ext
(dirName, fileName) = os.path.split(f) (fileBaseName, fileExtension)=os.path.splitext(fileName)
Run external program
if os.path.isfile(ausgabedatei) :
os.system("gnuplot " + ausgabedatei )
Checking Operating System
import os import sys if os.name == 'posix': print 'posix/Unix/Linux' elif os.name == 'nt': print 'windows' else: print 'unknown os' sys.exit(1)
Exceptions
Catch keyboard interrupt and do a "save exit"
try:
FILE = open("out.txt","w")
while 1:
i+=1
print i
except KeyboardInterrupt:
FILE.close()
Catch all exceptions
try: [...] except Exception, e: print "Exception raised: ", e
Custom Exceptions
try:
raise Exception('HiHo')
Debugging
Carsten Knoll wrote a nice module that improves the display of execeptions and allows to open an ipython shell at a certain point of the program code:
# ipHelp.py
# by Carsten Knoll
import sys
import new
__version__ = "0.2"
try:
from IPython.Shell import IPShellEmbed
args = ['-pi1','In <\\#>: ','-pi2',' .\\D.: ',
'-po','Out<\\#>: ','-nosep']
class AdaptedIPSE(IPShellEmbed):
def __init__(self, *args, **kwargs):
IPShellEmbed.__init__(self, *args, **kwargs)
old_interact = self.IP.interact # save the real method
def new_interact(self, *args):
self.IP.user_ns.update({'_ips_exit':False})
old_interact(*args) # call the real interact method
if self.IP.user_ns['_ips_exit']:
def do_nothing(*args, **kwargs):
pass
self.IP.interact = do_nothing
self.IP.interact = new.instancemethod(new_interact, self,
type(self))
IPS= AdaptedIPSE(args,
banner = 'Dropping into IPython',
exit_msg = 'Leaving Interpreter, back to program.')
def ip_syshook(pdb=0, mode=2):
import IPython.ultraTB
modus = ['Plain', 'Context', 'Verbose'][mode] # select the mode
sys.excepthook = IPython.ultraTB.FormattedTB(mode=modus,
color_scheme='Linux', call_pdb=pdb)
def ip_extra_syshook(fnc, pdb=0, filename=None):
assert callable(fnc)
import IPython.ultraTB
import time
if not filename == None:
assert isinstance(filename, str)
pdb = 0
ip_excepthook = IPython.ultraTB.FormattedTB(mode='Verbose',
color_scheme='Linux', call_pdb=pdb)
fileTraceback = IPython.ultraTB.FormattedTB(mode='Verbose',
color_scheme='NoColor', call_pdb=0)
def theexecphook (type, value, traceback):
fnc()
ip_excepthook(type, value, traceback)
# write this to a File without Colors
if not filename == None:
outFile = open(filename, "a")
outFile.write("--" + time.ctime()+" --\n")
outFile.write(fileTraceback.text(type, value, traceback))
outFile.write("\n-- --\n")
outFile.close()
sys.excepthook = theexecphook
from IPython.Debugger import Tracer
ST=Tracer()
except ImportError:
# create dummy functions
def IPS():
print "(EE): IPython is not available"
pass
def ip_syshook(*args):
pass
def ST():
pass
Now include this file in your project and place IPS() somewhere in your code to open a shell there.
from ipHelp import IPS, ip_syshook ip_syshook() # (1) -> debugger on exception # run IPS() somewhere to open ipython shell
If you have are unsing PyQT and you get the message "QCoreApplication::exec: The event loop is already running", inserting the following into your __init__ of your main class will help:
QtCore.pyqtRemoveInputHook()
