python ValueError invalid literal for float

Question

I ve a script which reads temperature data   def get temp socket  channels        data          for ch in channels          socket sendall  KRDG   s n    ch          time sleep 0 2          temp   socket recv 32  rstrip   r n            data ch    float temp    Sometimes  the script fails on the line which converts the values to float      File    projector py   line 129  in get temp   data ch    float temp    ValueError  invalid literal for float     135 057E 0    078 260E 0    00029   but this is NOT an invalid literal  If I enter this into any python shell   float  135 057E 0    then it correctly returns 135 057   So what is the problem

User · Accepted Answer

I would all but guarantee that the issue is some sort of non-printing character that's present in the value you pulled off your socket. It looks like you're using Python 2.x, in which case you can check for them with this:

print repr(temp)

You'll likely see something in there that's escaped in the form \x00. These non-printing characters don't show up when you print directly to the console, but their presence is enough to negatively impact the parsing of a string value into a float.

-- Edited for question changes --

It turns this is partly accurate for your issue - the root cause however appears to be that you're reading more information than you expect from your socket or otherwise receiving multiple values. You could do something like

map(float, temp.strip().split('\r\n'))

In order to convert each of the values, but if your function is supposed to return a single float value this is likely to cause confusion. Anyway, the issue certainly revolves around the presence of characters you did not expect to see in the value you retrieved from your socket.

User · Answer

I had a similar issue reading the serial output from a digital scale  I was reading  3 12  out of a 18 characters long output string   In my case sometimes there is a null character   x00   NUL  which magically appears in the scale s reply string and is not printed    I was getting the error    gt        0 00   gt  3 0 fast loop  delta    10 0 weight    0 0   gt        0 00   gt  1 800 fast loop  delta   10 0 weight    0 0   gt        0 00   gt  6 0 fast loop  delta    10 0 weight    0 0  gt        0 x00 0    gt  Traceback  most recent call last    gt    File  measure weight speed py   line 172  in start  gt      valueScale   float answer string    gt      ValueError  invalid literal for float    0   After some research I wrote few lines of code that work in my case   replyScale   scale port read 18  answer   replyScale 3 12  answer decode   answer replace   x00       answer strip   str answer decode strip    print repr answer strip   valueScale   float answer strip    The answers in these posts helped    How to get rid of  x00 in my array of bytes  Invalid literal for float    0 000001  how to fix error

User · Answer

Watch out for possible unintended literals in your argument   for example you can have a space within your argument  rendering it to a string   literal   float   0 33     After making sure the unintended space did not make it into the argument  I was left with   float 0 33     Like this it works like a charm    Take away is  Pay Attention for unintended literals  e g  spaces that you didn t see  within your input

[python] python ValueError: invalid literal for float()

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