Python: Trying to use "{}.replace()" with .format()

Question

A fairly simple question, but for the life of me I can't figure it out...

I have the following piece of code:

os.rename(FileName, FileName.replace(".png","")+"_"+time_stamp.replace(":","-").replace(" ","_")+"_"+name_string+".png")

Basically renaming an image file.

I want to use the .format() structure, but I can't figure out how to get the .replace() function to work with this.

At the moment my converted code looks like this:

os.rename(FileName, "{}.replace(".png","")_{}.replace(":","-").replace(" ","_")_{}.png".format(FileName,time_stamp,name_string))

At the moment the error being given is "invalid syntax" at the first replace ( a caret at the "" in (".png","")).

Could someone kindly point me in the right direction for resources to help with this?

Is there a better way of doing what I'm trying to?

Thanks

xiº · Accepted Answer · 2016-04-04 15:22:27Z

5

You shouldn't mix python string operation replace() with arguments for format().

os.rename(FileName, '{0}_{1}_{2}.png'.format(
    FileName.replace(".png", ""),
    time_stamp.replace(":", "-"),
    name_string.replace(" ", "_")
))

edited Apr 4, 2016 at 15:22

user824425

answered Apr 4, 2016 at 15:05

xiº

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2 Comments

Caitlin Over a year ago

Thank you very much! For some reason I was avoiding anything up the bare basics to the format() function, I'll definitely have to remember I can make it more complex.

Mike - SMT Over a year ago

You shouldn't mix ... I know this is an old post but can you maybe explain why?

Balaji Boggaram Ramanarayan · Accepted Answer · 2021-07-29 21:55:39Z

4

The basic form of the format you're using is this:

"Hello {}".format("there")

which evaluates to output string

"Hello there"

In its simple form, each {} in your string will get replaced by the strings in format, in order. More detailed info, you can find here: https://pyformat.info/

edited Jul 29, 2021 at 21:55

Balaji Boggaram Ramanarayan

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answered Apr 4, 2016 at 15:07

acdr

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Comments

someone · Accepted Answer · 2016-04-04 18:01:53Z

2

what are you need to do is

os.rename(FileName, "{0}_{1}_{2}".format(FileName.replace(".png",""), 
                                        time_stamp.replace(":","-").replace(" ","_"),
                                        name_string+".png"))

or more readable

newName = "{rmvFileFormat}_{time}_{addFileFormat}".format(rmvFileFormat = FileName.replace(".png",""), 
                                                          time = time_stamp.replace(":","-").replace("","_"),
                                                          addFileFormat = name_string+".png")
os.rename(FileName, newName)

answered Apr 4, 2016 at 18:01

someone

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Comments

Paulo Almeida · Accepted Answer · 2016-04-04 15:18:37Z

replace is a string method, you can't use it inside the string you're formatting. You would have to do:

s = "A {} string".format('very nice'.replace(' ', '_'))

if you wanted to replace only within the variable (which seems like your objective), or:

s = "A {} string".format('very nice').replace(' ', '_')

if you wanted to replace globally.

Regarding better ways of doing it, I would use os.path.splitext to split the extension, generate the time stamp already in the correct format (if you can control that, of course), instead of using the replace, and do all of that replacing before the os.rename part, so it's more readable (i.e. store the correct strings in variables and use those in the format, instead of doing it all in one line).

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