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How to slice a word in the label expression

PeterVersteeg

Hallo,

I have a field with city names and I want to slice the name in the label expression to only the 1st character.

I want to do this in python. looking at the internet i have this but it is not working:

def Label ( [CityName] 😞

s = [CityName]

s1 = s[1:]

return s1

i am working with arcgis for desktop 10.3.1

greetings Peter

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Accepted answers

FC_Basson

That's weird, because I tested the expression on a layer with Null values in the attribute filed and it worked. How about adding a None type check in there?

<SPAN class="keyword token">def</SPAN> FindLabel <SPAN class="punctuation token">(</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN> <SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp; <SPAN class="keyword token">try</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN> <SPAN class="keyword token">is</SPAN> <SPAN class="operator token">not</SPAN> None<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">:</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN>
&nbsp; <SPAN class="keyword token">except</SPAN> AttributeError<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">pass</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

All comments

FC_Basson

That's weird, because I tested the expression on a layer with Null values in the attribute filed and it worked. How about adding a None type check in there?

<SPAN class="keyword token">def</SPAN> FindLabel <SPAN class="punctuation token">(</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN> <SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp; <SPAN class="keyword token">try</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN> <SPAN class="keyword token">is</SPAN> <SPAN class="operator token">not</SPAN> None<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> <SPAN class="punctuation token">[</SPAN>CityName<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">:</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN>
&nbsp; <SPAN class="keyword token">except</SPAN> AttributeError<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">pass</SPAN>‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

PeterVersteeg

Your right there a NULL values and that was causing the error. My code works if I remove the NULL values but I need same on NULL.

your code is giving me the same error.

Greetings Peter

FC_Basson

It's probably due to an empty/Null attribute value, which could be returned as None. Try this definition expression:

<SPAN class="keyword token">def</SPAN> FindLabel <SPAN class="punctuation token">(</SPAN> <SPAN class="punctuation token">[</SPAN>CITY_CODE<SPAN class="punctuation token">]</SPAN> <SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
 <SPAN class="keyword token">try</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> <SPAN class="punctuation token">[</SPAN>CITY_CODE<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">:</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN>
 <SPAN class="keyword token">except</SPAN> AttributeError<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp; <SPAN class="keyword token">pass</SPAN>‍‍‍‍‍‍‍‍‍‍<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

FC_Basson

You could simplify the definition function even further:

<SPAN class="keyword token">def</SPAN> FindLabel <SPAN class="punctuation token">(</SPAN> <SPAN class="punctuation token">[</SPAN>CITY_CODE<SPAN class="punctuation token">]</SPAN> <SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> <SPAN class="punctuation token">[</SPAN>CITY_CODE<SPAN class="punctuation token">]</SPAN><SPAN class="punctuation token">[</SPAN><SPAN class="punctuation token">:</SPAN><SPAN class="number token">1</SPAN><SPAN class="punctuation token">]</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

PeterVersteeg

i stil got a string error

JoeBorgione

I got this to work:

def wtf (instring):
s= instring[:1] ####### Notice the position of the colon(:)
return s

Above is in the feild calculator, in a label expression be sure to choose python as the parser and check Advanced:

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