How can I extract a portion of a string using the SLICE function?

Summary:

I want to print only the first 7 characters but using the examples of the slicing funciont I wasn´t been able to do it.

for example in this case: Walmart Veracruz

I only want to print: Walmart

I have tested whit these expression but it did not work

"\~order_header.shipto_name"[slice([:7],len( "\~order_header.shipto_name "))]

"\~order_header.shipto_name"[slice((:7)),len( "\~order_header.shipto_name "))]

"\~order_header.shipto_name"[slice((0:-9)),len( "\~order_header.shipto_name "))]

functions={"slice": slice,("\~order_header.shipto_name"[:7])
{"slice": slice,("\~order_header.shipto_name"[:7])
{"slice": slice,("\~order_header.shipto_name"[:7])}

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