Pandas DataFrame fillna() Method
Example
Replace NULL values with the number 222222:
In this example we use a .csv file called data.csv
    import pandas as pd
df = pd.read_csv('data.csv')
newdf = df.fillna(222222)
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Definition and Usage
The fillna() method replaces the NULL values 
with a specified value.
The fillna() method returns a new DataFrame 
object unless the inplace parameter is set to 
True, in that case the 
fillna() method does the replacing in the original DataFrame instead.
Syntax
  
    dataframe.fillna(value, method, axis, inplace, limit, downcast)
  
Parameters
The axis, method,
inplace,
limit, downcast parameters are 
keyword arguments.
| Parameter | Value | Description | 
|---|---|---|
| value | Number String Dictionary Series DataFrame  | 
    Required, Specifies the value to replace the NULL values with. This can also be values for the entire row or column.  | 
    
| method | 'backfill' | 
    Optional, default None'. Specifies the method to use when replacing | 
| axis | 0 | 
    Optional, default 0. The axis to fill the NULL values along | 
| inplace | True | 
    Optional, default False. If True: the replacing is done on the current DataFrame. If False: returns a copy where the replacing is done. | 
| limit | NumberNone | 
    Optional, default None. Specifies the maximum number of NULL values to fill (if method is specified) | 
| downcast | DictionaryNone | 
    Optional, a dictionary of values to fill for specific data types | 
Return Value
A DataFrame with the result, or None if the inplace parameter is set to True.