What is the difference between python string concatenation and string insertion

Question

I want to know what is the diff between two string operations in python

filestamp = time.strftime('%Y-%m-%d')
database = "mysql";

Between this

filename = "/home/vmware/%s-%s.sql" % (database, filestamp)

and

filename = "/home/vmware/"+database+"-"+filestamp+".sql"

score 2 · Accepted Answer · 2011-05-22 06:57:19Z

2

String interpolation using the '%' operators take the types of the interpolated values into account. String concatentation using the '+' will only work for strings. So you can't mix strings with numbers using the '+' operator. In general: string interpolation is what you want - at least for building strings from other values especially if you deal with different types.

edited May 22, 2011 at 6:57

answered May 22, 2011 at 6:50

user2665694

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2 Comments

Mahakaal Over a year ago

If i use "+" am i committing any blunder , will my script work as expected . may be not efficent but will that cause any misfunctioning at any stage

user395760 Over a year ago

@Mahakaal: "a" + 1 gives TypeError: Can't convert 'int' object to str implicitly. class C(object): pass, "a" + C() gives TypeError: Can't convert 'C' object to str implicitly. However, some classes may define a __radd__ method that's basically return str(self) + some_str.

mechanicker · Accepted Answer · 2011-05-22 06:43:44Z

0

The first approach creates 1 string where as the second creates temporary strings which is wasted. Strings in python are immutable, once created you cannot modify it.

answered May 22, 2011 at 6:43

mechanicker

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3 Comments

Mahakaal Over a year ago

i don't understand "wasted" . i mean i am using in my program and they are working. whats problem in second. i am doing database backups in loop and its working. Under which case i can be in problem if i use second case

mechanicker Over a year ago

@Mahakaal: By wasted, I mean the temporary variables created between each concatenate operation is passed to the next and discarded. Each '+' creates a string variable that is used in the next (left to right) and discarded as it is no longer referred to. It works but not efficient.

user395760 Over a year ago

It's confusing to talk about "variables" here. There are "anonymous" string objects being created in between.

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