Python Programming

1==1.0 is True but 0.1+0.2==0.3 is False while(true): continue if ,break ,try,except exception as e \n print(e/customized error) except executes after a error occurs in try # try  may/may not be printed completely exception can be specified : except namerror:,except typerror:, valuerror:,zerodivisionerror raise error-type("error statement") else: gets executed if try was succcessful and no break statement finally: gets executed irrespective of error __name__ == __main__ by default or name of module used import filename  , filename.funcname , from filename import variablename(or)* global (used inside function) works on whole variable and can change its value global- used at top of prog , defined var can be used anywhere local -used inside a func to use that var in the func only enumerate(iterable) # add counter to an iterable and returns it.Syntax == for index,item in enumerate(iterable) list/set/dict comprehension ==  a=[1,2,5,1128938,3198,993,8589] # b=[] """ ...

 import module_name as alias For calling : module_name.func_name(arguments) Or from module_name import func1,func3 (or*)  For calling : func1(arguments)  func2(arguments) (Name Error)  dir(module_name) - describe all classes, functions and variables  Some default magic classes - builtins, cached, doc, file, loader, name, package, spec Note: Whenever a module is used in a program, its compiled file will be generated and stored in the hard disk permanently  Note: Custom made modules need to be in same folder as program or in default python path and this gets stored in variable PYTHONPATH While searching for modules when an import statement is used first preference is given to the folder the program is present in then python path and if not found even after that then an error.  LEGB Rule: Local, Enclosing, Global, Built-in  For passing arguments in a function in an indefinite order : Func1(arg2=value, arg1=val, arg3=val...)  A function can retur...

 Text Files - .txt,.c Binary files - .jpg,.dat f=open("file name",opening type) opening types: "r" - Read - Default value. Opens a file for reading, error if the file does not exist "a" - Append - Opens a file for appending, creates the file if it does not exist "w" - Write - Opens a file for writing, creates the file if it does not exist "x" - Create - Creates the specified file, returns an error if the file exists , [write only] r+,a+,w+  == read and write Difference between r+ and w+ (maybe) - r+ pointer at beginning and w+ pointer at end of file ‘rb’ will open for read in binary mode ‘rt’ will open for read in text mode Default is reading mode f.read()=variable f.close()= very imp to use after our work with a file is done f.read(n)==read first n characters f.readline()==read first line Writing it multiple lines allow it to read lines one by one  f.readline(n) - Read first n characters till the /n  If n is negative then it reads the ...

 camelCase PascalCase class PascalCase # always object = class()   to declare a object part of class and then perform functions memory is alloted only after the above step class ClassName:     class_attribute1=value1     attribute2=value2 object = ClassName() object_attribute= value # updates individual value or add new value object_attribute > class_attribule # more powerful(in times of calling them) self-> gets automatically replaced with object name # to use within a func in class self.variable object.fun()==class.fun(object) ** @staticmethod # written before def to make it as class.fun() # it is a decorator def __init__(self, {can contain more variable})==it gets automatically run even without calling when a object is created. eg. def __init__(self,a,b):                    self.a=a                    self.b=b object=class(5,80) the ab...

 JSON - dict format pickle - binary format variable=json.loads(dict enclosed in " " ) variable-type=dict variable2=json.dumps(dict) variable type=str use double inverted commas only json.dump(dict,file loc) variable3=json.load(file loc) same for pickling just replace json with pickle pretty print works with dump and dumps print(json.dumps(json_dict,indent=5,sort_keys=True)) example codes: CODE1 import json import requests def main():     data={         'username':"james",         'active':True,         'subscribers':10,         'orders_total':10.39,         'orders_ids':['abc','83m','hhd9']     }     # print(data)     s=json.dumps(data)     print(s)     print(type(s))     data2=json.loads(s)     # assert data2==data     print(data2)     # with open('file.json','w') as f:     ...

 raise error_name("message") ERRORS: NameError-undefined variable,mistype in variable/function name or name not enclosed in quotes TypeError- related to data types problems [eg. str doesn't work on int] ValueError-when a function gets wrong data type as input ZeroDivisinError AttributeError-using wrong methods or returning none/no return statement KeyError-dict IndexError IOError-file not found EOFError - end of file error FileNotFoundError IndentationError SYNTAX: try: except error1:runs if try has error1 except error2:runs if try has error2 Multiple exceptions can be specified in a except block. Eg except error1, error2 : else:runs if no error1 finally:always run, even if try block has return or break in it Python debugger module == pdb command prompt-$python-mpdbmycode.py pdb COMMANDS: l(lsit)-shows current position n(next)-next line excluding function s(step)-next line including function r(return)-steps to end of current executing function c(continue)-executes code q(...

 input print del  abs absolute value all() result true is all valid value , false if value contains false or 0 bin() converts to binary bool() format() getattr(class,"object") returns value of object of a class # also class.object iter and next # iterators len()  finds length list() open("file location") map() divmod(N1,N2) result == (quotient,remainder) filter() sorted() pow() power eg pow(4,2) == 4**2 range() reversed() round() type() zip() vars() __init__ eval('15+10')==25 # convert string to int or float accordingly id(variable)==place where variable is stored return == makes output of a function default input eg. def function(variable='something') try: sub part of function except: runs if try shoes error ** yield - generates a output as an object in memory continue: return back to the next iteration skipping any statement after it ord("alphanumeric")==ascii code chr(ascii code)==alphanumeric

LIST list=[1,2,"hello",4,5] l[position_index]=something -- update value of element slicing - also starts from 0 While performing slicing if we enter any out of bound values then it will not show an error.  FUNCTIONS: l.sort()= creates list in ascending order # eg. print(l.sort()) l.reverse()=reverse the order of elements in list l.append(something)== add new items at end of list(individual item 1 or multiple) l.insert(position_index,item to be added)== insert new item in between    [typeError if only 1 argument given] (if the positive index entered is bigger than list length then value gets added at last/end)  l.pop(position_index)==remove item [if nothing specified then last item]   [can give index error] pop function also returns the deleted element i.e. prints it in interactive mode(if used) l.remove(element in list)== remove first occurrence item [value error if not in list][type error if not specified] del l1[index/range]   [can give index er...

 Dictionary d={     "key1":"value1"     "key2":"value2" } d[key1] # output = value1  # will show error if key is incorrect Keys need to be of immutable data types eg, string,tuple or int  every key is unique,d is unordered [so no indexing]**,mutable Dictionary methods: d.keys()==print value of all keys as list (class=dict_keys) (list) output as dict_keys([list of keys]) d.values()==print all the values(list) output as dict_values([list of values]) d.items()== create a list of multiple tuples each having 2 elements :1 key and 1 value. output as dict_items([list of tuples]) d.update(d2)==add new item(s) of d2 in original dictionary at the end. or d[new_key]=new_value d.update("old_key","new_value")==replaces old value with new value d.get("key",error_message/value)== shows the related value or none # no error[default error message=None] print(d.get(...)) d.pop("key") d.clear() d.fromkeys(<a list of keys...

 A n escape sequence refers to a combination of characters beginning with a back slash (\) followed by letters or digits. Escape sequences represent non-printable and special characters in character and literal strings. As such, they allow users to communicate with a display device or printer by sending non-graphical control characters to specify actions like question marks and carriage returns. Credits for defination \\ backslash \' single quote \"double quote \a bell(plays beep sound) \b backspace \f formfeed(useless) \n linefeed(newline) \r carriage return(eg 1234567/rhello==hello67) \t horizontal tab \v vertical tab(useless) special charcters with their special meanings. occupies 1 charcter space