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Reading and writing CSV text files
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Variables are lost when a program ends. Text files let programs save data and load it again next time.
CSV files
A comma separated value (CSV) file stores one record per line, with fields separated by commas:
Ava,14
Ben,19
It is plain text, so many programs can read it.
Ava,14
Ben,19
It is plain text, so many programs can read it.
Reading a file
open(filename, "r") opens a file for reading.
A for loop reads one line at a time. strip() removes the newline at the end, and split(",") breaks the line into a list of fields.
Always close() the file when you are finished.
file = open("scores.txt", "r")
for line in file:
fields = line.strip().split(",")
print(fields[0], "scored", fields[1])
file.close()
A for loop reads one line at a time. strip() removes the newline at the end, and split(",") breaks the line into a list of fields.
Always close() the file when you are finished.
file = open("scores.txt", "r")
for line in file:
fields = line.strip().split(",")
print(fields[0], "scored", fields[1])
file.close()
Writing a file
"w" mode creates the file, or overwrites it if it already exists.
"a" mode appends: it adds to the end and keeps what is there.
write() does not add a new line by itself, so add \n.
file = open("scores.txt", "a")
file.write("Ravi,17\n")
file.close()
"a" mode appends: it adds to the end and keeps what is there.
write() does not add a new line by itself, so add \n.
file = open("scores.txt", "a")
file.write("Ravi,17\n")
file.close()
A line in a file is Ava,14,Leeds. What does line.split(",") give?
- split(",") cuts the string at every comma.
- Each piece becomes a list item.
Answer: ['Ava', '14', 'Leeds']
CSV files hold one record per line with comma-separated fields. Open with "r" to read, "w" to overwrite, "a" to append. Use strip() and split(",") to get the fields, then close() the file.
Check you have got it
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