pd.read_csv 没有创建具有适当属性的 dataframe

Question

I'm trying to get pandas to read as csv that's several million data entries large, and when I try to cut the data down to the relevant columns

It's early stages of the code, and can't proceed without the appropriate data

import pandas as pd


cols =  [1, 5, 6, 7, 10]
col_index = ["PGC", "GWGC", "HyperLEDA", "2MASS", "SDSS-DR12", "flag", "RA", "dec", "Luminosity Distance", "Distance Error", "Redshift", "Apparent B Magnitude", "B Magnitude Error",
"Apparent J Magnitude", "J magnitude error", "Apparent H Magnitude", "H Magnitude Error", "K Magnitude", "K Magnitude Error",
"Flag2", "Flag3"]#1, 5, 6, 7, 10]

df_cat = print(pd.read_csv("GLADE_2.3 - Copy.csv", chunksize = 10**8, index_col = col_index, usecols = cols))

print(df_cat.head())

AttributeError: 'NoneType' object has no attribute 'head'

It looks like the csv hasn't been read in successfully, and I'm aware that with such large files, it's probable that there could be a better way to handle the file - any and all suggestions appreciated

EDIT: Thank you so much to everyone who's answered! I really appreciate the help as I'm just trying to get to grips with pandas and keep mix-and-matching with built in modules

Answer 1

EDIT: nevermind... I didn't see that this has already been answered in the comments by @Kris and @ALollz.

It looks like your 'df_cat" is a string that results from a print statement. If you delete the print() statement that precedes the pd.read_csv(), I think it will work.

# delete the print statement here
df_cat = pd.read_csv("GLADE_2.3 - Copy.csv", chunksize = 10**8, index_col = col_index, usecols = cols)

# keep the print statement here
print(df_cat.head())

Answer 2

To expand on my comment above:

Try changing your code as follows:

import pandas as pd

cols =  [1, 5, 6, 7, 10]
col_index = ["PGC", "GWGC", "HyperLEDA", "2MASS", "SDSS-DR12", "flag", 
    "RA", "dec", "Luminosity Distance", "Distance Error", "Redshift", 
    "Apparent B Magnitude", "B Magnitude Error",
    "Apparent J Magnitude", "J magnitude error", "Apparent H Magnitude", "H 
    Magnitude Error", "K Magnitude", "K Magnitude Error",
   "Flag2", "Flag3"]#1, 5, 6, 7, 10]

df_cat = pd.read_csv("GLADE_2.3 - Copy.csv", chunksize = 10**8, index_col = col_index, usecols = cols)

df_cat.head()