How to use a while loop over a file to pass a search variable to a python pandas dataframe

I have two files: a Category file and a Spending file. I want to be able to set up a while loop to pass a variable from the Category file to a filter instruction for the Spending record. My spending category file (ecat) has a list of spending categories such as: “operations”, “marketing”, “”, “maintenance”, etc. The Spending file (outgo) has a table-like list of spending items like:

Date:Category:Amount:Remarks (**those are the headings)
     Date     Category     Amount                     Remarks
0   201101:   Operations:     200.00:                   paperwork
1   201201:   Operations:     190.00:                   who knows
2   210109:  Contractors:    1050.00:        Political assessment
3   201001:  Engineering:    2550.00:               new equipment
4   201203:   Operations:  300000.00:               land purchase

My filter command is like this:

df=pd.read_csv('outgo',delimiter=':')

So, the while loop I have set up is as follows:

 with open('ecats', 'r') as catfile:
          cat=catfile.readline()
          while cat:
            print(cat)
            x=df[df.Category.str.contains(cat)]
            print(x)
            cat=catfile.readline()

The problem seems to be that the “cat” variable is not being passed to the filter instruction. It returns an empty dataframe[].

The print command duly prints out which category is being accessed as the while loops through the file but the variable gets lost or blocked somewhere on the way to the filter command x=df[df.Category.str.contains(cat)].

Is there some obvious reason while the cat variable is not being passed into the filter command?

Pardon the long-winded and lurid description but it has been frustrating that something seemingly straightforward will not perform.