# Meaning of xf

**URL:** <https://discourse.julialang.org/t/meaning-of-xf/114009>\
**Category:** New to Julia\
**Created:** [May 8, 2024, 3:58pm UTC](https://discourse.julialang.org/t/meaning-of-xf/114009 "2024-05-08T15:58:02Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![ssrrii](https://avatars.discourse-cdn.com/v4/letter/s/838e76/32.png) [@ssrrii](https://discourse.julialang.org/u/ssrrii)\
**Post date:** [May 8, 2024, 3:58pm UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/1 "2024-05-08T15:58:02Z")

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I try to better understand how to write to and read from xlsx-files. But also to better understand the syntax and idea behind it.

For writing to a file the function is given:  
XLSX.openxlsx(wb\_path, mode=“rw”) do xf  
… end  
For reading from a file is given:  
XLSX.openxlsx(“myfile.xlsx”, enable\_cache=false) do f  
… end  
What do ‘xf’ and ‘f’ stand for? Maybe a silly question, but I could not find an explanation sofar. Hope you can clarify this.

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**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [May 8, 2024, 4:09pm UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/2 "2024-05-08T16:09:11Z")

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They are just arbitrary variable names with no special significance.

Take a look at [the manual for more info on `do` block syntax](https://docs.julialang.org/en/v1/manual/functions/#Do-Block-Syntax-for-Function-Arguments) and also see [this discussion](https://discourse.julialang.org/t/do-block-syntax-examples/40757).

In short, `do` blocks are an alternative syntax for creating and passing an anonymous function as the first argument to another function. The following are equivalent:

```julia
foo(x -> bar(x), y) # anonymous function with `->` syntax

# is equivalent to

foo(
    function (x) # notice that we didn't give this function a name
        bar(x)
    end,
y) # anonymous function with `function` syntax

# is equivalent to

foo(y) do x
    bar(x)
end # anonymous function created and passed via `do` syntax

```

There isn’t any significance to the name `x` here, it’s just the name given to the argument of the anonymous function. The `xf` and `f` in your case are similarly just names.

In this case, based on (what I’m guessing about) the `XLSX.openxlsx` function, I’m betting that they are file handles that can be used to access the contents of the file. The reason that an anonymous function is used here is to ensure that the file gets closed once the code is done reading it (or, importantly, if it stops reading because it throws an error).

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**Author:** ![Nathan\_Boyer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nathan_boyer/32/14825_2.png) [@Nathan\_Boyer](https://discourse.julialang.org/u/Nathan_Boyer)\
**Post date:** [May 8, 2024, 4:50pm UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/3 "2024-05-08T16:50:16Z")

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You can use any variable name you like, but `xf` likely stands for “Excel file” and `f` for “file”. You then pass the variable name for the file, defined after the word `do`, to the other functions in the `do` block to lay out what operations you want to perform on the file while it is open.

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<div class="post-metadata">

**Author:** ![ssrrii](https://avatars.discourse-cdn.com/v4/letter/s/838e76/32.png) [@ssrrii](https://discourse.julialang.org/u/ssrrii)\
**Post date:** [May 10, 2024, 11:57am UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/4 "2024-05-10T11:57:29Z")

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Thanks, this helps to understand. I’ll dive more into anonymous functions.

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<div class="post-metadata">

**Author:** ![ssrrii](https://avatars.discourse-cdn.com/v4/letter/s/838e76/32.png) [@ssrrii](https://discourse.julialang.org/u/ssrrii)\
**Post date:** [May 10, 2024, 11:59am UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/5 "2024-05-10T11:59:10Z")

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OK, so xf and f just refer to the first argument of the function.

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<div class="post-metadata">

**Author:** ![Nathan\_Boyer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/nathan_boyer/32/14825_2.png) [@Nathan\_Boyer](https://discourse.julialang.org/u/Nathan_Boyer)\
**Post date:** [May 10, 2024, 1:37pm UTC](https://discourse.julialang.org/t/meaning-of-xf/114009/6 "2024-05-10T13:37:45Z")

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Yeah, well, other way around. The functions in the `do` block refer to output of the `openxlsx` command which is often named `xf`. (I name it `file` below.)

Here is an alternative and not recommended method that may illustrate what is happening better:

```julia
using DataFrames, XLSX
df = DataFrame(
    A = [1, 2, 3, 4, 1],
    B = ["M", "F", "F", "M", "O"],
)
filepath = "./xlsxtest.xlsx"
file = XLSX.openxlsx(filepath, mode="w")
sheet = file[1]
XLSX.writetable!(sheet, df1)
XLSX.writexlsx(filepath, file) # this line is not needed in the `do` block version
close(file) # this line is not needed in the `do` block version

```

The `do` version defines all the commands in the middle as an anonymous function and then passes that anonymous function into the `openxlsx` function. That way the opening, reading/writing, and closing all happens in one step. It is less error-prone and faster that way.