Why use files in Python?¶
Often, your program needs to work with data in files - you don't want to make the user input a whole bunch of values every time they use it.
Examples:
- analyzing weather data
- generating payroll
- saving progress and returning to it later (like in a Word processor)
Opening files in Python¶
Python provides a built-in open() function which will returns a new type with a scary name like _io.TextIOWrapper.
#assumes the gettysburg.txt file is in
#the same directory as your .py file
gettysburg_file = open("gettysburg.txt")
type(gettysburg_file)
For our purposes, just think of the variable gettysburg_file as a variable which represents a file object.
Making sure your files are in the right place¶
Reading data from files¶
Python files work with several different methods that allow you to read data.
read()reads the file into a big stringreadline()reads the next line of the file into a stringreadlines()reads the lines of the file into a list of strings
gettysburg_file = open("gettysburg.txt")
file_contents = gettysburg_file.read()
print(file_contents)
gettysburg_file = open("gettysburg.txt")
firstline = gettysburg_file.readline()
secondline = gettysburg_file.readline()
print(secondline)
gettysburg_file = open("gettysburg.txt")
contents_as_list = gettysburg_file.readlines()
print( contents_as_list[8] )
Opening files using with statements¶
Opening files with a with statement does the same thing, but it does some nice things like closing the file when it is done.
with open("gettysburg.txt") as gettysburg_file:
gettysburg_text = gettysburg_file.readlines()
print(gettysburg_text)
print("All done with the file.")
Analyzing Baby Names Example¶
Let's say we want to analyze baby name popularity, and we have a file with data from https://www.ssa.gov/oact/babynames/decades/names2010s.html
with open("top_male_baby_names_2010s.txt") as male_names_file:
male_names = male_names_file.readlines()
print(male_names)
It's annoying that the newline character \n is included in all of the strings. To remove these, you could use the rstrip() string method.
name = "Eric\n"
name
name.rstrip()
looping through and removing all the newlines¶
with open("top_male_baby_names_2010s.txt") as male_names_file:
male_names = male_names_file.readlines()
name_counter = 0
while name_counter < len(male_names):
male_names[name_counter] = male_names[name_counter].rstrip()
name_counter += 1
print(male_names)
Now we can use Python to ask interesting question of our data¶
Here's a program that lets the user check how popular a name was.
name_to_search = input("Enter a name: ")
if name_to_search in male_names:
position = male_names.index(name_to_search)
print(name_to_search,"was the number",(position+1),"most popular male name in the 2010s.")
else:
print(name_to_search,"was not a popular name in the 2010s.")