Python strings and its place holders

 We all learnt what are  the python strings. Like concatenation,  repeating one strings in multiple times. Hope that blog has impressed you. If you want to look at the blog Previous.

Today's related to strings and but a step forward to the before blog. That is placeholders .

Context 

• Indexing 
• Slicing 
• Placeholders

Indexing 

          It is one of the operation in string. It is also a numbering given to letter in words in sentence. It is useful to access the characters in the string individually.

Sen = "charan loves apples" # declaring a str

Indexing of a strung takes places like this 

c h a r a n    l o v e s    a p p l e s .

^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^     

0 1 3 4 5 6 7 8 9 ..............

Even the space holds a index too .  

This is how the indexing pattern. 

If you comes in reverse (from last ) of the sentence.

c h a r a n    l o v e s     a  p  p  l  e  s 

^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^  ^  ^  ^  ^  ^ 

                                       -6 -5 -4 -3 -2 -1      

This is the theory. 

Program 

sen = "charan loves apples"

sen[0]    #accessing the first  letter

Sen[4]   # accessing the fifth letter 

This is how we do the indexing in the python. 

Slicing 

            In indexing,  we can only access one character.That makes slicing come into picture to access a word in string or  a part of a word.

Syntax:

Var[SI : EI]

Where :

    Var = string variable.

     SI  = Starting Index 

     LI  =  Ending Index

Here , EI is omitted.see the example you will get the clarification.

sen = "charan loves apples"

# let's try to get one word i.e, "charan".

sen[0:6] # here sixth index is holded by space

sen[0:5] 

Let's try to do it in program.

In the above pic  you can see the ending index is not taken to count. 

Let us move on to next topic

Placeholders 

            Why we have to use placeholders . If we want to use sentence (or) a string for different bames or number. 

Let's take a example 

Same sentence that is 

sen = "charan loves apples. If other friends like same apples too. 

Gokul and vignesh even likes the apples . 

We can't write 

"Gokul loves apples"

"Vignesh loves ..... "

And another friend that is why we use placeholders. 

We use some substitutes for each data types. 

In above example,  we are only changing the name of a person rest of thr lle string is same. So, we have to use substitutes for only person name .

Substitutes for all data types :

String  -> %s

Integer -> %d

Float.   ->  %f

Double -> %lf 

Characters -> %c

Let's see application of concept 

sen = "%s loves apples"

sen%("charan") # substituting word with %s

sen%("vignesh")

Now ,we will see  double variable placeholders . Substituting two variables. 

Eg

sent  = "%s%s loves apples"

sent%("charan","vignesh")

If you want to get the gap between names. Maintain gap between substitutes. 

Let's see combination of stting and integer. 

app  = "%s is %d years old :

app%("Irfaan",18)

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