27rohitb.github.io

Basic

This module contains snippets of code/info. which are easier to forget and can come in handy later.

String functions:

Tells us where is “str” located in whole of the str.
NOTE: that if “str” is NOT present in str, then it WILL throw and ERROR!!

str.index("str")

Replace “old” with “new” in str if “old” present.

str.replace("old", "new)      

Return a bool if only “a” sub-string is present in “str”

"a" in "str":

Number functions:

Remainder of (a/b)

a % b

Round off to min(given number)

floor(3.7) = 3

Round off to max(given number)

ceil(2.3) = 3

Input functions:

Inputs stuff from user DEFAULT input is takes as STRING

str_var = input("str")

Eval will check what is the data type (int/float/complex) and convert input data to that

num_var = eval(input("number"))

List functions:

Start indexing from the end and given the number at “index”.

list_var[-index]

Gives all the element from “start_index” up till “end_index” (EXCLUDING thing at end_index)
NOTE: that start/end_index = null/nothing, which means from/till start/end

list_var[start_index : end_index]

Appends/merge two lists
NOTE: its NOT same as append which is used to add data “into” the list

list_var.extend(list2_var)

Inserts data at the given index_no

list_var.insert( index_no, data )

Remove the last element and return it

list_var.pop()

Returns the INDEX of data

list_var.index( data )

Returns a copy of the list

list2_var = list_var.copy()

Tuple functions:

() -> Tuples

These are used when you dont want the data to change, say for example coordinates. Similar to list, just without modification functions or fancy indexing.

Dictionary functions:

{} -> Dictonary will be made only if key:value is given, otheriwse it will creates a set.

Mostly used to make converter or map something (for eg, expander of “jan” to “january”)

NOTE: In KEY-VAL pair. KEY must be unique and Value MUST be hasbable.

Return value for the given key, if it exists.

dict_var[KEY]

retun default_val if key is NOT found, only valid for this.

dict_var.get(KEY, default_val) 

Other stuff:

CATCHING ERRORS:

Best practise:

• Use Specific Errors mostly.
• Put specific exceptions at the top.

syntax:

try:
	#code here
except ZeroDivisionError as err:
	#Do something
	#as err-> STORES error into variable "err"
except <any error by default>:
	#TODO for everything else
else:
	#TODO if no exception is found
finally:
	#TODO independent of an error or not

Raise general exception on demand

raise Exception

FILE IO:

Most common way to open read the file line by line (this automatically closes the file after reading:

with open(cfile_name,"r") as fin:
	line = fin.readline()

Return a BOOL val depending upon the readability of the file.
NOTE is ALSO depends upon the MODE inwhich file was opened (r/r+/w)

file_var.readable()

Returns a LIST of lines in the file which was read #NOTE its readLINES and NOT readLINE.

file_var.readlines()

a: append mode to file; w: Overwrites!! file

open("filename","a/w")

If filemode is append, then it adds “data” to last line.
NOTE: it does NOT adds newline.

file_var.write( data )