Basic questions

1. what is lambda function?
   in line function
   x= lambda a,b: a*b
2. built in data types in python
   • text
   • number
   • list
   • dict
   • set
   • bool
   • bytes
3. DICTIONARY
   note : no comma at last items

    dict = {"a":10, "b":20}   
    for x in dict #here x is key only.  
    for x in dict.keys() #key  
    for x in dict.values() # values  
    for x,y in dict.items() # key values
   

   for copy newdict = thisdict.copy or newdict = dict(thisdict)

4. try except

    try:  
        print("Hello")  
    except:  
        print("Something went wrong")  
    else:  
        print("Nothing went wrong")
   

   here else will be executed if except doesnt execute.
   try except finally can be used too finally will execute no matter exception occurs or not
   raise can be used for throwing exception.
   Examples: python raise Exception("Sorry, no numbers below zero") raise TypeError("Only integers are allowed")

5. Input
   myinput = input() pythong 2.7 uses raw_input.
6. String format examples [useful]

   txt = "The price is {} dollars for {} itmes"  
   print(txt.format(10,5))  
   myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars."  
   # 0 1 2 for index and :.2f for 2 point pafter decimal.  
   myorder = "I have a {carname}, it is a {model}."  
   print(myorder.format(carname = "Ford", model = "Mustang"))  
   

7. decorator function This is basically a function inside another function. and innerfunction is returned by outer function.
   *args and **kwargs can be used to transparently pass the argument
   example:

    def calculate_time(func):
        def inner1(*args,**kwargs):
            begin = time.time()
            func(*args,**kwargs)
            end = time.time()
            print("total time taken: ",func.__name__,end-begin)
        return inner1
    #usage here
    @calculate_time
    def fact(num):
        print(math.factorial(num))
    fact(100)
   

   chaining of decorator is also possible.

8. common mistakes

   x =a or b if a false x will be equal to b whatever it is
   x= a and b if a true x will be equal to b whatever it is

code example

copy file from one to other

with open('data') as input_file, open('result', 'w') as output_file:
  for line in input_file:
    output_file.write(parse(line))

args kwargs

def myFun(*args,**kwargs):
	print("args: ", args)
	print("kwargs: ", kwargs)
myFun('geeks','for','geeks',first="Geeks",mid="for",last="Geeks")

my learnings.

Pandas
numpy
scipy

External links:

pdf cheat sheet
shortcuts in python
python lists