I want to modify beta and n2 in Test.txt. However, f0.write() is completely rewriting all the contents. I present the current and expected outputs.
fo = open("Test.txt", "w") fo.write( "beta=1e-2") fo.write( "n2=5.0") fo.close() The contents of Test.txt is
beta=1e-1 n1=30.0 n2=50.0 The current output is
beta=1e-2n2=5.0 The expected output is
beta=1e-2 n1=30.0 n2=5.0 First you need to read the contents of the file and store it on a dictionary, preferably using the with statement:
data = {} with open('Test.txt') as f: for line in f: line = line.strip() # Ignore empty lines if not line: continue # Split every line on `=` key, value = line.split('=') data[key] = value Then, you need to modify the read dictionary to the contents you want:
data['beta'] = 1e-2 data['n2'] = 5.0 Finally, open the file again on write mode and write back the dictionary:
with open('Text.txt', 'w') as f: for key, value in data.items(): # Join keys and values using `=` print(key, value, sep='=', file=f) 
in <module> key, value = line.strip().split('=') ValueError: too many values to unpack (expected 2)
Here an another example.
# get the data in the file fo = open("Test.txt", "r") data = fo.read() fo.close() # Put the data in a list stripped = data.split('\n') # A dict with the data that you want to rewrite modification = { "beta": "1e-2", "n2" : "5.0" } # Loop in the list, if there is a key that match the dict, it will change the value for i in range(len(stripped)): name = stripped[i].split("=")[0] if name in modification: stripped[i] = name + '=' + modification[name] fo = open("Test.txt", "w") fo.write("\n".join(stripped)) fo.close() 