python: DataFrame.append does not append element

Question

I am working one week with python and I need some help. I want that if certain condition is fulfilled, it adds a value to a database. My program doesn't give an error but it doesn't append an element to my database

import pandas as pd
noTEU = pd.DataFrame() # empty database
index_TEU = 0
for vessel in list:
    if condition is fullfilled:
        imo_vessel = pd.DataFrame({'imo': vessel}, index=[index_TEU])   
        noTEU.append(imo_vessel) # I want here to add an element to my database
        index_TEU = index_TEU + 1

If I run this, at the end I still get an empty dataframe. I have no idea why it doesn't do what I want it to do

It is not an inplace operation. Try `noTEU = noTEU.append(imo_vessel)` — ayhan, Sep 16 '16 at 15:58
Do we have a canonical question for this? Not specific to append but in general, for methods returning a new dataframe? — ayhan, Sep 16 '16 at 15:59
@ayhan there are a ton of questions with the same answer but there isn't a canonical one, it should be created as it gets tiresome explaining this — EdChum, Sep 16 '16 at 16:00
There's a similar one asked over here: http://stackoverflow.com/questions/16597265/appending-to-an-empty-data-frame-in-pandas — Nickil Maveli, Sep 16 '16 at 16:02
@NickilMaveli yeah that might be a good target for this question but I don't know if we could use it if the question was about, say, drop instead of append. It might be better if someone posted a general question about this. — ayhan, Sep 16 '16 at 16:07
@ayhan: Totally agree with that. Even the docs don't indicate whether `append` operation takes place `inplace` or not. — Nickil Maveli, Sep 16 '16 at 16:12

score 1 · Accepted Answer · answered Sep 16 '16 at 15:59

You should reassign the dataframe such as:

import pandas as pd
noTEU = pd.DataFrame() # empty database
index_TEU = 0
for vessel in list:
    if condition is fullfilled:
        imo_vessel = pd.DataFrame({'imo': vessel}, index=[index_TEU])   
        noTEU = noTEU.append(imo_vessel) # I want here to add an element to my database
        index_TEU = index_TEU + 1

and don't use the keyword list for a List because it's included in the Python syntax.

python: DataFrame.append does not append element

1 Answers1