Python Diaries Chapter 1

  Divyanshu Bansal  |    June 20, 2018

Python 2.x<br> ## To print in Python ``` print 'Hello, World!' ``` ``` Output --> Hello, World! ``` ## Comments ``` '''This is a comment.''' ``` ``` # This is also a comment ``` ***hash*** is used for single line comment and ***triple quotes*** for multiple lines ## To input an integer in Python ``` n=input() ``` ## To input String ``` a=raw_input() ``` ## To create an empty array(*list* in Python) ``` arr=[] ``` ## To assign a value to all elements of an array Let us say you wanna make an array of size 10 with each element equal to 0 ie. same value to all ``` arr=[0]*10 ``` ``` output --> [0,0,0,0,0,0,0,0,0,0] ``` ## To add item in array(*list*) ``` arr.append(1) arr.append(2) print arr ``` ``` output --> [1,2] ``` ## while loop syntax ``` i=0 l=10 while i<l: print i i=i+1 ``` ## for-in loop syntax ``` arr=[1,2,3,4] for item in arr: print item ``` ``` #output will be each array item printed in separate line ``` *you can use any thing instead of item like a,b,c it,key ie.literally anything except keywords and reserved words* ## To print *print* statements in same line, just add a comma after your text ``` print 'Next print statement after this will be printed in same line', print "I'm in first line" ``` ``` Output-->Next print statement after this will be printed in same line I'm in first line' ``` ## Variant of for in loop. *If you want to loop from i=start to end let us say 1 to 10* ``` for i in range(1,11): print i ``` in **range(start,end)**--> ***start* is inclusive and *end* is exclusive**, read like this **[start,end)** If you don't pass an argument, **default** **value**--> **start = 0,end=len(string)** if you want to jump by n then range(start,end,jump=n), default value --> **jump=0** ## To sort an array(both integer and string) ``` arr=[7,6,4,9,3,2,8,1,5] arr1=sorted(arr) arr2=sorted(arr,reverse=True) ``` ``` # output arr1 --> [1,2,3,4,5,6,7,8,9] # output arr2 --> [9,8,7,6,5,4,3,2,1] ``` **NOTE --> In Python, when using true-false, remember to CAPITALIZE FIRST LETTER ie. *True* and *False*** *logical operators just type name in english ie. && --> and , || --> or , ! --> not*<br> *bitwise operators are same as C ie. & , | , ^(XOR)*<br> *all arithmetic operators are also same as in C*<br> ## if-else in Python ``` a=5 if a==5: print "Sweet Mother of Mercy!" elif a==6: print "It's a SIX" elif a==4: print "It's a FOUR" else: print "Not an interesting number" ``` ``` Output --> Sweet Mother of Mercy! ``` ## ========Various types of Inputs======== **If you have to input a variable** ``` n=input() ``` **If you have to input a character or string (including spaces)** ``` a=raw_input() ``` **If you want to store words in an array, for eg. if the line is --> save this line in an array** ``` arr=map(str,raw_input().split()) ``` ``` output --> ['save','this','line','in','an','array'] ``` **If you want to store integers in an array for eg. --> 5 7 3 2 62 7 8** ``` arr=map(int,raw_input().split()) ``` ``` #output --> [5,7,3,2,62,7,8] ``` **If you want to input a line/word and store each character seperately eg.--> divyanshu** ``` a=list(raw_input()) ``` ``` #output --> ['d','i','v','y','a','n','s','h','u'] ``` **To acces an particular index in array** ``` print a[0] print a[1] ``` ``` ouput--> 'd' output --> 'i' ``` *similarly for other indices* **Suppose you input an integer as a string, now you want to convert it to integer use this** ``` a='5' a=int(a) ``` **To convert an integer to string** ``` b=5 b=str(5) ``` **To join all items of an array** ``` arr=['d','i','v','y','a','n','s','h','u'] c=''.join(arr) ``` ``` output will be--> 'divyanshu' ``` **To reverse an array or string** ``` a='example' arr=['d','i','v','y','a','n','s','h','u'] b=a[::-1] arr=arr[::-1] ``` ``` output --> 'elpmaxe' similarly for array (feeling too tired to type ;-) ) ``` That's it for now......<br> Next article will be posted soon....*stay tuned !* <br> [1]: http://www.github.com/algolover

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