Useful python commands

PythonCheatSheet.py

# I use python so infequently that i forget most of the stuff i learnt when next I need to use it.
# Here are some frequently used commands. Python 3.5 NOT 2.7

# System variables:

__file__
# Absolute path to current script

# Basic Syntax:

class Object(InheritedObject):
# define class that inhereits from another class
	def function(arguments):
		pass
	# member function
	def __init__(self, master=None):
	# constructor
        InheritedObject.__init__(self, master)
		# call constructor from inhereited class
		self.variable = 0
		# member variables
		
if __name__ == "__main__":
# if you want to use python file like a library this won't be called.
	obj = Object()
	obj.function()
	
### SYS ###
import sys

for arg in sys.argv:
	# ignore file argument
	if arg == __file__: 
		continue
	if arg == "argument":
		pass
# Handling command line arguments
sys.exit("""optional return int""")
# exit script. 

### FILE IO ###

# open a file with permissions. "r" = reading, "w" writing, "r+" reading and writing, "a" appending, "b" binary mode, "t" text mode
with open('workfile', "rwb") as f:
# above automatically closes file, otherwise close manually
f = open('workfile')
f.close()
# read file to string in text mode, or bytes in binary mode
f.read()
# seek file position
f.seek(0)

### JSON ###
import json 

with open("file.json", "r") as json_file:
    json_str = json_file.read()

json_obj = json.loads(json_str)
# do stuff here. json_obj is a regular dictionary object. 
with open("map_model.json", "w") as json_file:
	# use dumps format dict to file back to a json formatted str. 
    json_file.write(json.dumps(json_obj))  

### ARGPARSE ###

parser = argparse.ArgumentParser(formatter_class=argparse.RawDescriptionHelpFormatter,
                                 description=textwrap.dedent('''Discription'''),
                                 epilog='''Written by Peter Respondek''')
parser.add_argument("-r", help="directories will be relative to this position")
# optional argument
parser.add_argument("root", help="start directory")
# positional argument
argv = parser.parse_args()
var = argv.r
# get -r argument

### OS ###
import os

os.chdir
# Change the current working directory to path.
os.utime("path", None)
# touch time modified tim
os.remove("path/to/file")
# delete file
path = os.getcwd()
# current working directory

### OS.PATH ###

os.path.isfile("path/to/file")
# check if file exists
os.path.exists("path/to/file")
# check if path exists
name,ext = os.path.splitext("filename")
# Split filename and extension
path,file = os.path.split("path")
# Split filename and file dir
time = os.path.getmtime("filename")
# Get file modified time
path = os.path.relpath("/path/to/file1", "/path/to/file1")
# Relatve path between two directories
path = os.path.expanduser("~/path/to/file")
# Get absolute path to file which has user shortcut
path = os.path.join("path","filename")
# join two paths
for (dirpath, dirnames, filenames) in os.walk("path"):
# recursively iterate through path 


### SUBPROCESS ###
import subprocess

returncode = subprocess.call(['command', 'args'])
# make system call and wait for it to finish.
subprocess.check_call(['command', 'args'])
# make system call and wait for it to finish. raise CalledProcessError if it doesn't work.

### RE ###

### TKINTER ###
import Tkinter

# use file extenstion .pyw for scripts using tkinter to automatically open GUI

class Application(Frame):
	def __init__(self, master=None):
		Frame.__init__(self, master)
		self.grid(sticky=N+S+E+W)
		Grid.rowconfigure(self, 0, weight=1, minsize=70)
        	Grid.rowconfigure(self, 1, weight=1, minsize=70)
		Grid.columnconfigure(self, 0, weight=1)
        	Grid.columnconfigure(self, 1, weight=1)
		
		frame = LabelFrame(self, text="Frame Name")
        	Grid.columnconfigure(frame, 0, weight=1)
		Grid.rowconfigure(frame, 0, weight=1)
		frame.grid(row=0, padx=5, columnspan = 2, pady=5, sticky=N+S+E+W)
		
		scrollbar = Scrollbar(frame)
        	scrollbar.grid(row=0,column=1,padx=(0,5),pady=5, sticky=N+S+E+W)
        	self.console.config(yscrollcommand=scrollbar.set)
        	scrollbar.config(command=self.console.yview)
		
		button = Button(frame, text = "Button", command = buttonFunction)
		button.config(state="active", relief=RAISED)
        	button.grid(row=1,column=0,padx=5,pady=5, sticky=N+S+E+W)
		
		listbox = Listbox(frame)
		listbox.bind("<Up>", self.function)
		#bind input to function
		
		textbox = Text(frame, wrap=NONE)
        	textbox.tag_config("intro", foreground="blue")
        	textbox.insert(END,"TEXT!")

root = Tk()
root.title("App Name")
root.minsize(600,600)
Grid.rowconfigure(root, 0, weight=1)
Grid.columnconfigure(root, 0, weight=1)
app = Application(master=root)
root.protocol("WM_DELETE_WINDOW", app.shutdown)
app.mainloop()
# basic setup