#!/usr/bin/env python
# coding: utf-8

# # Reading Files
# 
# Python provides built-in functions for reading and writing files.  

# To read a file, we must know the path of the file on the disk. Python has a module called `os` that has helper functions that helps dealing with the the operating system. Advantage of using the `os` module is that the code you write will work without change on any suppored operating systems.

# In[ ]:


import os


# To open a file, we need to know the path to the file. We will now open and read the file `worldcitites.csv` located in your data package. In your data package the data folder is in the `data/` directory. We can construct the relative path to the file using the `os.path.join()` method.

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data_pkg_path = 'data'
filename = 'worldcities.csv'
path = os.path.join(data_pkg_path, filename)
print(path)


# To open the file, use the built-in `open()` function. We specify the *mode* as `r` which means read-only. If we wanted to change the file contents or write a new file, we would open it with `w` mode.
# 
# Our input file also contains Unicode characters, so we specify `UTF-8` as the encoding.
# 
# The open() function returns a file object. We can call the  `readline()` method for reading the content of the file, one line at a time.
# 
# It is a good practice to always close the file when you are done with it. To close the file, we must call the `close()` method on the file object.

# In[ ]:


f = open(path, 'r', encoding='utf-8')
print(f.readline())
print(f.readline())
f.close()


# Calling `readline()` for each line of the file is tedious. Ideally, we want to loop through all the lines in file. You can iterate through the file object like below.
# 
# We can loop through each line of the file and increase the `count` variable by 1 for each iteration of the loop. At the end, the count variable's value will be equal to the number of lines in the file.

# In[ ]:


f = open(path, 'r', encoding='utf-8')

count = 0
for line in f:
    count += 1
f.close()
print(count)


# ## Exercise
# 
# Print first 5 lines of the file. 
# 
# - Hint: Use break statement

# In[ ]:


import os
data_pkg_path = 'data'
filename = 'worldcities.csv'
path = os.path.join(data_pkg_path, filename)

# Add code to open the file and read first 5 lines


# ----